Add some params docstring to create_server
Add some params docstring to create_server

Basically we don't describe all available params on the docstring to
avoid maintenance burden, but we add some params to the method which
calls "create a server" API because the API is most useful in whole
OpenStack APIs, and the added params are mandatory in most use cases.

Change-Id: If15080b5950c98207c10de2839c724fda07ff91f

vedujoshi/tempest,sebrandon1/tempest,Tesora/tesora-tempest,openstack/tempest,openstack/tempest,masayukig/tempest,Tesora/tesora-tempest,masayukig/tempest,vedujoshi/tempest,cisco-openstack/tempest,Juniper/tempest,cisco-openstack/tempest,Juniper/tempest,sebrandon1/tempest