Add DTL autotests

[kinvaris]

Test possible DTL configuration with a single or multiple storagedrivers in a vpool:

BASIC: 5b3d30e

• Configuring a DTL with only 1 storagedriver to a non existing location (should fail scenario); blocked by vPool with 1 storagedriver can configure DTL but it shouldn't framework#1417
• Configuring a DTL with 2 storagedrivers
• When deploying a vdisk, the DTL should be configured in the primary or recovery DC based on choice: security or speed?
• Shutting down a node with a vdisk with sync DTL will be testing in the HA autotests; tested by Add HA autotests #427

ADVANCED:

• Shutting down a proxy, writing some data to the vdisk, starting the proxy again, trigger volumedriver restart_from_dtl, checking if the written data on the vdisk is still present. (currently only works in the same datacenter only)

[JeffreyDevloo]

Fixed by #460