NetApp fix ssc volume filtering inconsistency

This fixes the situation when the actual netapp
volume data structure becomes inconsistent
because of operating on the actual object
than the copy of it. It also introduces some checks
before calculating volume stats.

Change-Id: I626f9ca9aa8c7cc41ba4aa6058f14cc040f7301f
Closes-Bug:#1243081
(cherry picked from commit 1d503937e841da27f5e3441775b2d208e44f5e75)
Merge "NetApp fix ssc volume filtering inconsistency" into stable/havana