Browser test speed and reporting improvements.
Browser test speed and reporting improvements.

- test runs print a URL where job details can be viewed
- only one browser session is created for the entire test run, as opposed to
  one *per test* before
- the user name of the current user is added to the test run as a tag

R=gary.poster, matthew.scott
CC=
https://codereview.appspot.com/7300054

jrwren/juju-gui,jrwren/juju-gui,mitechie/juju-gui,mitechie/juju-gui,CanonicalJS/juju-gui,mitechie/juju-gui,bac/juju-gui,jrwren/juju-gui,bac/juju-gui,jrwren/juju-gui,CanonicalJS/juju-gui,mitechie/juju-gui,bac/juju-gui,CanonicalJS/juju-gui,bac/juju-gui