[autotest] Change os.path.join use in common.py to be portable.

All uses of |os.path.join("x", "../..")| have been changed into
|os.path.join("x", "..", "..")|.

TEST=syntax check all common.py files, trybot passes HWTest
BUG=None

Change-Id: Ic05a2e375352eab4447ae5b180da750ccbc1b914
Reviewed-on: https://gerrit.chromium.org/gerrit/40312
Tested-by: Alex Miller <milleral@chromium.org>
Commit-Queue: Scott Zawalski <scottz@chromium.org>
Reviewed-by: Scott Zawalski <scottz@chromium.org>
Commit-Queue: Alex Miller <milleral@chromium.org>
28 files changed