Make common->compute->shelve_server param more clear
Make common->compute->shelve_server param more clear

common->compute->shelve_server() function accept the
compute server client as first arg but it is not clearly named
or mentioned in doc string.

This will improve this function usage and will be helpful
if it will be defined as lib interfacein future.

Change-Id: I5b9a18b005f620d7eca2e52d8bbc90e9d4f95502

cisco-openstack/tempest,masayukig/tempest,Juniper/tempest,openstack/tempest,cisco-openstack/tempest,vedujoshi/tempest,openstack/tempest,masayukig/tempest,Juniper/tempest,vedujoshi/tempest