Bug 991657 - [v1.3] Backport test_cards_view_with_two_apps.py test to v1.3

Replace test_cards_view_launch_app.py and test_cards_view_with_three_apps.py with the above test
Include a number of changes to gata_test from master which are needed
Pin to marionette-client 0.7.1.1 which is needed for v1.3
Bug 991653 - [v1.3] Backport test_power_button_long_press.py test to v1.3

This pulls in a commit for:
Bug 968751 - Write a test to open long-press power button menu
Merge pull request #17988 from bobsilverberg/cards_view_v1.3

Bug 991657 - [v1.3] Backport test_cards_view_with_two_apps.py test to v1.3
Merge pull request #17991 from bobsilverberg/power_button

Bug 991653 - [v1.3] Backport test_power_button_long_press.py test to v1.3