iscsi: allow for multipath setup

[smitterl]

Some tests need to simulate a multipath setup.
For this add a new parameter. If it is allowed to create multipath the export function that creates the iscsi objects will ignore if a backstor/fileio of the given name already exists.

[smitterl]

Tested manually:

>>> params_1 = {'emulated_image': '/var/tmp/em1', 'target': 'iqn.2025-02.com.virttest:device.em1.target', 'image_size': '1G', 'portal_ip': '127.0.0.1', 'enable_authentication': False, 'iscsi_allow_multipath': 'yes'} 
>>> params_2 = {'emulated_image': '/var/tmp/em1', 'target': 'iqn.2025-02.com.virttest:device.em2.target', 'image_size': '1G', 'portal_ip': '127.0.0.1', 'enable_authentication': False, 'iscsi_allow_multipath': 'yes'} 
>>> _iscsi_1 = iscsi.Iscsi.create_iSCSI(params_1)
>>> _iscsi_2 = iscsi.Iscsi.create_iSCSI(params_2)
>>> _iscsi_1.login()
>>> _iscsi_2.login()

results in

# targetcli ls
o- / ......................................................................................................................... [...]
  o- backstores .............................................................................................................. [...]
  | o- block .................................................................................................. [Storage Objects: 0]
  | o- fileio ................................................................................................. [Storage Objects: 1]
  | | o- device.em1 ................................................................... [/var/tmp/em1 (1.0GiB) write-back activated]
  | |   o- alua ................................................................................................... [ALUA Groups: 1]
  | |     o- default_tg_pt_gp ....................................................................... [ALUA state: Active/optimized]
  | o- pscsi .................................................................................................. [Storage Objects: 0]
  | o- ramdisk ................................................................................................ [Storage Objects: 0]
  o- iscsi ............................................................................................................ [Targets: 2]
  | o- iqn.2025-02.com.virttest:device.em1.target ........................................................................ [TPGs: 1]
  | | o- tpg1 .................................................................................................. [gen-acls, no-auth]
  | |   o- acls .......................................................................................................... [ACLs: 0]
  | |   o- luns .......................................................................................................... [LUNs: 1]
  | |   | o- lun0 ............................................................ [fileio/device.em1 (/var/tmp/em1) (default_tg_pt_gp)]
  | |   o- portals .................................................................................................... [Portals: 1]
  | |     o- 0.0.0.0:3260 ..................................................................................................... [OK]
  | o- iqn.2025-02.com.virttest:device.em2.target ........................................................................ [TPGs: 1]
  |   o- tpg1 .................................................................................................. [gen-acls, no-auth]
  |     o- acls .......................................................................................................... [ACLs: 0]
  |     o- luns .......................................................................................................... [LUNs: 1]
  |     | o- lun0 ............................................................ [fileio/device.em1 (/var/tmp/em1) (default_tg_pt_gp)]
  |     o- portals .................................................................................................... [Portals: 1]
  |       o- 0.0.0.0:3260 ..................................................................................................... [OK]
  o- loopback ......................................................................................................... [Targets: 0]

and it also cleans up well:

_iscsi_1.cleanup()
_iscsi_2.cleanup()

# targetcli ls
o- / ......................................................................................................................... [...]
  o- backstores .............................................................................................................. [...]
  | o- block .................................................................................................. [Storage Objects: 0]
  | o- fileio ................................................................................................. [Storage Objects: 0]
  | o- pscsi .................................................................................................. [Storage Objects: 0]
  | o- ramdisk ................................................................................................ [Storage Objects: 0]
  o- iscsi ............................................................................................................ [Targets: 0]
  o- loopback ......................................................................................................... [Targets: 0]

[meinaLi]

During my test with auto case, the error message is "Storage object fileio/device.emulated-iscsi exists". So to cover all related message, maybe we can change it to file_exists = re.match( r".*storage object.*exists.*", str(e), re.DOTALL | re.IGNORECASE ) .

[smitterl]

Thank you, @meinaLi Fixed, please review again.

[meinaLi]

The word "already" and the : after exist also need to be removed. Otherwise, the absence of these in the message will cause errors.