Disable some image_test cases with concurrent collector.

The following image_test cases sometimes fail on ART Builbot's
x86 concurrent collector configuration:
- ImageTest.WriteReadUncompressed
- ImageTest.WriteReadLZ4
- ImageTest.WriteReadLZ4HC
Disable them to make the build turn green again, while we
investigate the failures.

Bug: 27578460
Change-Id: I46126e4690e6300e3bfa771c1b6a560272ecb1da