Update keystone auth-url when service becomes available

Fixes #252

Signed-off-by: Adam Stokes <adam.stokes@ubuntu.com>
Update 'using juju in openstack doc' to remove updating
environments.yaml

This is done automatically now

Signed-off-by: Adam Stokes <adam.stokes@ubuntu.com>
make async method explicit

Signed-off-by: Adam Stokes <adam.stokes@ubuntu.com>