Updated from global requirements

Change-Id: Icb3c49781f2769698714d4fab9cbaed10ebe4251
Tidy up xenapi/volume_utils.py

Removed unused code and made some private methods start with _

Change-Id: Idae0bf55b9d0586fd0a0412aace517afc46031ea
Move tests into test_volume_utils

Move some tests in test_xenapi that would fit better in
test_volume_utils.

Change-Id: Ibe516a2473ff921d4f43621e71645810e674f73b
Merge "Tidy up xenapi/volume_utils.py"
Merge "Move tests into test_volume_utils"
Merge "Updated from global requirements"