Disable test_pack.py unit test until it works on Travis-CI and for Python 2.7.
Disable test_pack.py unit test until it works on Travis-CI and for Python 2.7.

mbedmicro/pyOCD,mbedmicro/pyOCD,mesheven/pyOCD,mesheven/pyOCD,pyocd/pyOCD,mesheven/pyOCD,mbedmicro/pyOCD,pyocd/pyOCD,flit/pyOCD,flit/pyOCD