Add max microversion = 2.42 for compute host tests

This is to add max_microversion = 2.42 for compute host tests
as the API in question is deprecated from 2.43 onward [0].
This is also consistent with Tempest [1].

Also adds a test for test_show_host to be consistent with [1] but
not any other endpoints as those are too risky to run Patrole side or have
various warnings associated with them in the API documentation [0].

[0] https://developer.openstack.org/api-ref/compute/#hosts-os-hosts-deprecated
[1] https://github.com/openstack/tempest/blob/28b252f7f61a2dfc585089265cdb3118defbcfff/tempest/api/compute/admin/test_hosts.py#L23

Partially Implements blueprint: clear-deprecated-api

Change-Id: Ifceb5d4656a76bf865f8ef494fc1b093b626cfe0
1 file changed