Integration tests - base class for all tests

The TestCase class will be the base for all tests, except the login
tests.
It contains two methods:
setUp - opens the login page, and performs the login to allow all test
start from the home page.

tearDown - returns the driver to the home page and logs out.

https://wiki.openstack.org/wiki/Horizon/Testing/UI

Partially implements blueprint: selenium-integration-testing

Change-Id: I748174108844c26eab0d375dafcd1f429f0e83dc
Merge "Integration tests - base class for all tests"