Bug 804515 - Add screen orientation commands to Marionette

setScreenOrientation allows for a subset of the permitted orientation
change values that screen.mozLockOrientation can take.  Specifically
portrait, landscape, portrait-primary, landscape-primary,
portrait-secondary, landscape-secondary.

Due to W3C bug 23950 both error replies use the non-descriptive 500
status code.  I've filed bug 945734 about this.
---
 testing/marionette/client/marionette/marionette.py | 47 +++++++++--
 .../tests/unit/test_screen_orientation.py          | 90 ++++++++++++++++++++++
 .../client/marionette/tests/unit/unit-tests.ini    |  2 +
 testing/marionette/marionette-server.js            | 50 +++++++++++-
 4 files changed, 183 insertions(+), 6 deletions(-)
 create mode 100644 testing/marionette/client/marionette/tests/unit/test_screen_orientation.py