fixed variable name

[ghost]

ceph_pool_plugin threw an exeption which shows in syslog as

Feb 16 08:29:29 ceph00 collectd[4416]: ceph-pool: failed to ceph pool stats :: global name 'ceph_dfcmdline' is not defined :: Traceback (most recent call last):#012  File "/usr/share/collectd/python/ceph_pool_plugin.py", line 57, in get_stats#012    df_output = subprocess.check_output(ceph_dfcmdline, shell=True)#012NameError: global name 'ceph_dfcmdline' is not defined
Feb 16 08:29:29 ceph00 collectd[4416]: ceph: failed to retrieve stats

I found that "ceph_dfcmdline" was actually called "cephdf_cmdline".

[waipeng]

Can confirm this works. Please merge this, thanks!

[A-Dechorgnat]

+1

[cgimeno]

Confirmed

[Kallio]

Please merge this. IT has also duplicate req #42 and #41

[dbiazus]

👍