Move get_server_ip into tempest.common.compute

This will be required by the new wait_until={PINGABLE|SSHABLE} logic
within the module so move this down from
tempest.api.compute.base.BaseV2ComputeTest.

A version of this is also present in tempest.scenario.manager however
unifying that with this version is left for another change.

Change-Id: Iddfdf48da58320844e265fb1209e25a53d501f93
2 files changed