Fix snapshot GC test

Changes to object store removes SecondaryStorage host from the host
table. This affects the test where we identify the secondary storage nfs
host to login to where we verify if the snapshot is present on the
physical resource.

* added base classes for imagestore/stagingstore operations
* fixed the test to check only if NFS is used as backing store

TODO: Fix for s3 based storage layer

Signed-off-by: Prasanna Santhanam <tsp@apache.org>
(cherry picked from commit 4f973778bf6c2bfc7da2b8c785557e86f81af9d5)
remove local path in cloud-set-guest-password script

Signed-off-by: Prasanna Santhanam <tsp@apache.org>
(cherry picked from commit 2d4e17e8d4c25775448af7f76b4eb61e4e56bf3f)
Fix snapshot limit tests

Signed-off-by: Prasanna Santhanam <tsp@apache.org>
(cherry picked from commit 79cd3df6fb13210cfdb1cf0058737d912629c856)