Add "--remote-source" option to "volume snapshot create" command
to support creating snapshot from an existing remote snapshot in
volume v2 (v2 only), also add the doc, unit tests and release note.

Change-Id: I9e5fad4f0db5b44d528eb6b930edbc816e392c3a
Implements: bp cinder-command-support
Closes-Bug: #1618676
Co-Authored-By: Sheel Rana <ranasheel2000@gmail.com>

Add '--force' option to 'volume snapshot delete' command in
volume v2 (v2 only) to allow delete in state other than error
or available.

Change-Id: Ie8991e9a630d7c7e9ac6c6870aed787bbcebacf2
Closes-Bug: #1597195

Add "--name", "--status" and "--volume" options
to "volume snapshot list" command for filtering results.

Change-Id: I72db1abce7701f31598deec34801a4d1f5713870
Closes-Bug:#1645252

1.change the command name ``snapshot create/delete/list/
show/set/unset`` to ``volume snapshot create/delete/list/
show/set/unset``.

2.change the optional parameter "--name <name>" to a
positional parameter "<snapshot-name>"; Change the
positional parameter "<volume>" to a optional
parameter "--volume <volume>"

Change-Id: If03276ecdf6f0d96893d5ecf91c2aaa64929cff3
Implements: bp backup-snapshot-renamed-for-volume-resource
Co-Authored-By: Sheel Rana <ranasheel2000@gmail.com>

Support multi REST API calls error handling for
"snapshot set" command follow the rule in
doc/source/command-errors.rst. Also add a unit
test for testing the error handling

Change-Id: I0c6214271bc54a25b051c0a62438c3344c8b51d7

this will better isolate the unit tests from the functional tests.
unfortunately, the "integration" tests had to be lumped into the
"unit" tests since we need the separation in testr.conf

Change-Id: Ifd12198c1f90e4e3c951c73bfa1884ab300d8ded