heat common : BaseClient respect host argument

Currently the BaseClient class ignores any host argument and overwrites
it with the host from the keystone catalog URL, we should respect the
host parameter if it is passed, but make it optional

ref bug 1102101

Change-Id: I371e3b70a7bd207a177625c3e6855d8504678f1b
Merge "heat common : BaseClient respect host argument"