Make compute api use util.check_string_length
Make compute api use util.check_string_length

Make some string variables check in compute use util.check_string_length
instead of checking by itself

Change-Id: I9a5d4f647611aa00bed44afdeda5763f8fa9c35b

openstack/oslo.versionedobjects,citrix-openstack-build/oslo.versionedobjects