testing: Update MakeEnvironment to take CofingAttrs

Update the testing factory function MakeEnvironment to take a new parameter: ConfigAttrs. ConfigAttrs is a map of environment configuration attributes which override the factory defaults.
Merge branch 'master' of https://github.com/juju/juju into makeEnv-take-config
Merge branch 'master' of https://github.com/juju/juju into makeEnv-take-config
Merge pull request #1310 from waigani/makeEnv-take-config

testing: Update MakeEnvironment to take CofingAttrs

Update the testing factory function MakeEnvironment to take a new parameter: ConfigAttrs. ConfigAttrs is a map of environment configuration attributes which override the factory defaults.

(Review request: http://reviews.vapour.ws/r/625/)