ART: Disable libcore tests failing on bots

Some tests in previous commits are failing on the testing devices.
Tests dependent on DateTimeFormatter fail on hammerhead due to
misconfigured locales and tests with a server running on localhost
fail due to the loop device being switched off on volantisg. These
problems will be further investigated but this patch disables them
for the time being.

Change-Id: I2dde178925de555f26a4d532be15487f499571b4