Add `snapshots` key support for quota class update

Fix bug 1188452

Change-Id: I3db0f3f1191a24571de9631786889ee81af777f6
python3: Fix traceback while running tests

The testsuite is full of the following:

TypeError: 'dict_keys' object does not support indexing

This is due to the fact in python3 dict methods dict.keys(),
dict.items() and dict.values() return “views” instead of lists.

Change-Id: Ifa5383e6485fdbabf363fd1442877b2452346c1c
Signed-off-by: Chuck Short <chuck.short@canonical.com>
Merge "Add `snapshots` key support for quota class update"