Merge ~kissiel/checkbox-support:xrandr-rotation-improv into checkbox-support:master

[Maciej Kisielewski]

xrandr: fix crashing when DISPLAY is not defined

Tested by running "from checkbox_support.contrib import xrandr" with and without having DISPLAY defined in environ.

[Sylvain Pineau (sylvain-pineau)]

+1

review: Approve

diff --git a/checkbox_support/contrib/xrandr.py b/checkbox_support/contrib/xrandr.py
index eee9c4e..9a79f40 100644
--- a/checkbox_support/contrib/xrandr.py
+++ b/checkbox_support/contrib/xrandr.py
@@ -977,6 +977,8 @@ class Screen(object):
 def get_current_display():
     """Returns the currently used display"""
     display_url = os.getenv("DISPLAY")
+    if display_url is None:
+        raise SystemExit("DISPLAY environment variable is not defined!")
     open_display = xlib.XOpenDisplay
     # Set .argtypes and .restype, to ensure proper
     # type check and conversion