test_croppedSource flaky test

[Timo Jyrinki]

It seems the test qmltestrunner::ScopeStyle::test_croppedSource() is flaky, which causes automatic testing failures and delays for unity 8 reverse dependencies.

An example at
https://objectstorage.prodstack4-5.canonical.com/v1/AUTH_77e2ada1e7a84929a74ba3b87153c0ac/autopkgtest-vivid-ci-train-ppa-service-landing-059/vivid/amd64/u/unity8/20160512_013332@/log.gz

---
********* Start testing of qmltestrunner *********
Config: Using QtTest library 5.4.1, Qt 5.4.1 (x86_64-little_endian-lp64 shared (dynamic) release build; by GCC 4.9.2)
PASS : qmltestrunner::ScopeStyle::initTestCase()
FAIL! : qmltestrunner::ScopeStyle::test_croppedSource() property width
   Actual (): 40
   Expected (): 0
   Loc: [/tmp/adt-run.nSE58n/build.UFP/unity8-8.12+15.04.20160504.2/tests/plugins/Dash/tst_CroppedImageMinimumSourceSize.qml(48)]
PASS : qmltestrunner::ScopeStyle::cleanupTestCase()
Totals: 2 passed, 1 failed, 0 skipped, 0 blacklisted
********* Finished testing of qmltestrunner *********
---

(automatic testing for ubuntu-system-settings silo)

[Michał Sawicz (saviq)]

Note it's actually CroppedImageMinimumSourceSize, not ScopeStyle (bad copy/paste).