[TestChangeProcessGroup] Mark the test as xfail for Android API 16

Summary:
This change adds the infrastructure to mark tests as xfail for specific
Android API levels.

Test Plan: dotest.py TestChangeProcessGroup on an Android API 16 device.

Reviewers: chying, labath, chaoren

Reviewed By: labath, chaoren

Subscribers: tberghammer, lldb-commits

Differential Revision: http://reviews.llvm.org/D10261

llvm-svn: 239126