In volume snapshot command, <volume> is the same
as <snapshot-name> when --volume is not specified,
but <volume> cannot be None, so when <snapshot-name>
is not specified (<snapshot-name> is None), a NoneType
error appears.
So make <snapshot-name> no longer optional, it should
be always present.

Change-Id: I3d9f10753a8ef601e70816421c160598e2cc811f
Closes-bug: #1659894

Supporting "--no-property" option will apply user a convenient
way to clean all properties of volume snapshot in a short command,
and this kind of behavior is the recommended way to devref.
The patch adds "--no-property" option in "volume snapshot set" command,
and update related test cases and devref document.

Change-Id: I5f10cc2b5814553699920c4343995b2e11416e4e
Implements: blueprint allow-overwrite-set-options

In network_qos_rule_type.py, network_service_provider.py, server.py and
volume_snapshot.py, the description format is using """ """.
In this patch, the former format is replaced with "_description = _( )".

Change-Id: I6863b01d3534e033df745070037ee45286745c92

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>