After applying schema validation to volume actions
APIs[1], error messages are formatted as per the
standards. So the tests are failing because of error
messages.

This patch fixes failed functional tests by correcting
error messages.

[1]https://review.openstack.org/#/c/559042/

Change-Id: Id05bf637d77ab401fc0aec5be09eee423bf1a223

Enforce ordering of imports with H306.

For tests, this is mostly done by grouping test
imports after other cinderclient imports.

Change-Id: Ie40fda014d1aedb057e5b4ea1f27f999c84e6373

The behaviour of PY3's standard lib 'argparse'
differs from PY2's.

```
cinder extend 2
usage: cinder extend <volume> <new_size>
error: too few arguments
Try 'cinder help extend' for more information.

cinder extend 3
usage: cinder extend <volume> <new_size>
error: the following arguments are required: <new_size>
Try 'cinder help extend' for more information.

```
This could lead to the partly failure of functional testcase,
fix it.

Change-Id: I59e9ae149af0b4294b09a94a52a4bc86a1d90f2b
Closes-Bug: #1697428

Negative tests for the cinder CLI commands which check actions with
volume extend command like extend volume without arguments or with
incorrect arguments and check that correct error message raised.

Change-Id: Ic7c846fa2d8e7c867ed575d922b4a7e935120705