Adds support for microversion 2.54 which adds resetting keypair and
unsetting keypair in rebuild operation.
Adds optional ``--key-name`` and ``--key-unset`` options
in the ``nova rebuild`` command.
The ``--key-name`` and ``--key-unset`` cannot be specified
at the same time.
Change-Id: Ie2a39bb29dd59c070adc94e79ea0f6473227a427
Implements: blueprint rebuild-keypair-reset