Support including tests/suites from other autotest directories.

This change allows autotest packages (server-package, control files, suites) to
include files in other autotest directories.

BUG=b:28319891
TEST=local build, run_suite
test with CL:
https://android-review.googlesource.com/#/c/219615/
run `m dist`
Go to out/autotest
Run test:
site_utils/test_droid.py -r 100.96.51.111 -s 2c462228 dummy_PassServerDragonboard

Change-Id: I35f241900e039a19be82a1b1d0a5be63e97f766e
1 file changed