Workarounding screen edge test breaks xrandr test

Workarounding bug #1522466 in a test (a problem with screen edges without XRandr) unfortunately breaks another test that was passing without the workaround:

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17/18 Test #17: kwin-testXRandRScreens ...........***Exception: Other 1.23 sec
********* Start testing of TestXRandRScreens *********
Config: Using QtTest library 5.5.1, Qt 5.5.1 (x86_64-little_endian-lp64 shared (dynamic) release build; by GCC 5.2.1 20151129)
QFATAL : TestXRandRScreens::initTestCase() Received signal 11
FAIL! : TestXRandRScreens::initTestCase() Received a fatal error.
   Loc: [Unknown file(0)]
Totals: 0 passed, 1 failed, 0 skipped, 0 blacklisted
********* Finished testing of TestXRandRScreens *********
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This should be fixed. One option is to wait for the real Qt upstream fix for the bug #1522466 (screen edges without xrandr) and remove the workaround at that point. The workaround itself is harmless since only test setup is changed.