NetApp:iSCSI drivers reserved percent need to change to 0.

The iscsi drivers reserved percent is 100 as of now. This needs
to be changed to 0 for default values. It needs to be corrected
so that filter scheduler does not discard netapp backend.

bug 1182015

Change-Id: Id80584e5d478c83de97735706994206e024f8bf6
Adds create_from_volume test cases

  For tests.test_volumes,
  added 3 test cases:
     create_from_volume
     create_from_volume_with_glance_metadata
     create_from_volume_failed_on_cloning
  refactored an internal api:
     _create_volume_from_image

  The reason not to test a non-exist volume as source_vol is
  the uplayer(volume api) has already checked and ensured the
  source_vol exists

Change-Id: I9c345bc29cae31f1a22236a4849f13d7289ea49e
Merge "NetApp:iSCSI drivers reserved percent need to change to 0."
Merge "Adds create_from_volume test cases"