Manila has used single gigabytes quota for shares and snapshots.
Config opt 'no_snapshot_gb_quota' is set to False by default, that has been
used for enabling/disabling of snapshot gigabytes quota considerations.
Add separate snapshot gigabyte quota and remove opt 'no_snapshot_gb_quota' that
is not needed anymore. To be able to set infinite quota for snapshot gigabytes,
just set value for new config option 'quota_snapshot_gigabytes' to '-1'.
Change-Id: I43cb95ff3d0d3e6191f520b52edb67a0a44e9c2c
Implements BP add-snapshot-gb-quota