invocation: support loading pytest module for pytest_name='x.y.z'

To make the naming of pytest more flexible, now LoadPytestModule
supports pytest_name containing dots. If pytest_name does not contain
any dot, will falls back to old implementation.
For example, we currently have a lot of ec_xxx tests, they can now become
  ec/battery.py    (pytest_name='ec.battery')
  ec/lightbar.py   (pytest_name='ec.lightbar')
  etc...

BUG=None
TEST=test on DUT w/ old test list, run_pytest w/ and w/o goofy, make test

Change-Id: I3bc14cd8ea244d9febeaca8c4e8c6d7612984b8b
Reviewed-on: https://chromium-review.googlesource.com/320528
Commit-Ready: Wei-Han Chen <stimim@chromium.org>
Tested-by: Wei-Han Chen <stimim@chromium.org>
Reviewed-by: Hung-Te Lin <hungte@chromium.org>
5 files changed