Current compute_client.servers.create() relies on block_device_mapping
arg which is legacy[1]. "block_device_mapping" format require
device_name which is leads to hard-coded hack in --volume key handler
to KVM specific. "block_device_mapping_v2" format is more friendly
to hypervisiors.
Support of block_device_mapping_v2 appear in python-novaclient 2.16.0,
openstackclient require at least 2.29.0

Makes options --volume and --block-device-mapping work simultaneously.
Appends --block-device-mapping data even if --volume used.
After bug 1383338 only --volume was taken when both are used.

[1]http://docs.openstack.org/developer/nova/block_device_mapping.html

NOTE(dtroyer): I moved the new test_boot_from_volume() functional
test to Ie51b1c375c5940856ec76a5770df3c6bd18a3eba to test our
previous behaviour.  The only changes required to support the new
behaviour should be that the empty_volume is now attached in that test.

Change-Id: I7bac3d870dd9ca404093142f8bce22a62e49180d
Closes-Bug: 1647406
Closes-Bug: 1497845

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