Updated acceptance test README
Updated acceptance test README

* Removed Rackspace-specific environment variables.
* Added OS_POOL_NAME environment variable.
* Added OS_NETWORK_NAME environment variable.
* Added bash function for test shortcuts.
* Added notes about compute tests.

feiskyer/gophercloud,jamiehannaford/gophercloud,feiskyer/gophercloud,jamiehannaford/gophercloud