Add test case for showing host details

Tempest has provided test for listing volume hosts, but lacks test
for showing details of a volume host. This patch adds the support.

Including:
[1] Add show host API to volume v2 hosts_client library
[2] Add release note
[3] Add test case for showing volume host details
[4] Add unit tests for hosts_client API
[5] Fix for test_list_hosts

Change-Id: I72e91bb86fbc65083aceb59a59b0a375904c7678
4 files changed