Update shrink scenario tests

This patch updates the shrink scenario tests to handle with the
"available" or "shrinking_possible_data_loss_error" state received
from the manila share manager after a failed shrink operation when
attempt to shrink a share with a size smaller than thecurrent used
space.

Change-Id: Idf34a149e5a975d5fbced0ec78d102c5d90b87c6
Related-Bug: #1858328
3 files changed