Add share snapshots at db level

Change-Id: I376bf37d845e35f6396f2e5f28e3ab272c1ca23a
NetAppShareDriver: changed export prefix of path

Change-Id: I8df6598d56c98e5bd9a5e77d53b72f7d013a4eb0
NetAppShareDriver: make name of func short

Change-Id: Id75dac3e0f597e05cfa593320ea5e554ef83c1a5
Share Snapshots implementation

Change-Id: I5a98b1a0a1ea03eeefd90fe5f1c4eec81076f3ce