Split OkHttp tests from other libcore tests

Having one CTSv2 module for most of libcore is
potentially causing flakiness. This commit pulls
out OkHttp tests into a separate module called
CtsLibcoreOkHttpTestCases.

Bug: 29384784
Bug: 29181264
Change-Id: I6fbab91911914ba10c4dd32113e409a0ed4c17e8
4 files changed