Handle Firefox Account creation. (#30)

This pr is for issue #30, please keep in mind that is WIP pr and I have to rebase it after pr #32 get's landed.

Notes:
I packaged the fxa-python-client and I install it with `pip install fxa-python-client-1.0.0.tar.gz`, so I don't have to do other hacks (to move over the setup.py location and to return, to install git on slaves or to clone the workspace from another job and to exlude the trigger.py when removing the repository)
The tradeoff of this was that I had to make a requirenmens text file and install them with pip install -r

Because we have to add the credentials in config file before ve have an environment, I declare the at the top of the script and create the account just before I ran the testrun. If an exception is thrown and we fail to create the account the build will be aborted, so this is safe. 

For a uid at emai creation I made use of BUILD_TAG variable because is the only one is unique, the BUILD_ID is the timestamp and when running concurrent builds it might duplicate.
https://wiki.jenkins-ci.org/display/JENKINS/Building+a+software+project#Buildingasoftwareproject-below

If we want to install it via `pip install fxa-python-client-1.0.0.tar.gz` we have to install the requirements separately. it wont install them by it's own. If we want them to be installed by the setup.py, we have to clone the repo change the directory, call `python setup.py install` but this is even more ugly. as I mentioned in notes. I searched about this and I've got feedback from Bebe fro webqa. 
As I sayd the alternative would be to create a job to clone the github repo clone the workspace and call `setup.py install`