nova: support query hosts with availability-zone

[Robin5911]

For #2188

nova: add support query hosts with availability-zone parameter

Filter the server list result by server availability zone.

This parameter is restricted to administrators until microversion 2.83. If non-admin users specify this parameter on a microversion less than 2.83, it will be ignored.

[coveralls]

Coverage remained the same at 79.762% when pulling c33b5bb on TonyZhang1989:master into 1875fb8 on gophercloud:master.

[theopenlab-ci]

Build succeeded.

• gophercloud-unittest : SUCCESS in 4m 07s
• gophercloud-acceptance-test : SUCCESS in 2h 44m 24s
• gophercloud-acceptance-test-ironic : SUCCESS in 50m 57s

[EmilienM]

please squash the commits or rebase, so we have one single commit.

[jtopjian]

@EmilienM Squashing can be done via GitHub. Multiple commits within PRs are actually preferred here since it's easier to see revisions.

However, per the contributor's tutorial, the following items need addressed in this PR:

1. A corresponding issue needs to be opened that describes the issue or feature.
2. The Nova code that implements this feature on the server-side.