Add ability for cbuildbot to only run unit tests for revved packages.

Add ability for cbuildbot to only run unit tests for revved packages.

Change-Id: I6744aac09fb075f91f710f16343fab45b8dc8af9

BUG=chromium-os:7283
TEST=Ran it with cbuildbot through the unit tests phase and looked
at the file and saw it get parsed correctly.

Committed: http://chrome-svn/viewvc/chromeos?view=rev&revision=e483618

[petkov, 2010-11-22 20:05:23]

LGTM w/ a suggestion.

Also, reading through the issue -- update_engine added a few minutes to the test
run but much less than 10 -- the rest of the tests take time to build/run. For
one, it seems that most of the test builds don't pass -j16 (or ${MAKEOPTS}
through scons).

http://codereview.chromium.org/5124006/diff/1/cros_run_unit_tests
File cros_run_unit_tests (right):

http://codereview.chromium.org/5124006/diff/1/cros_run_unit_tests#newcode65
cros_run_unit_tests:65: if [ -z "${FLAGS_package_file}" -a -z
"${FLAGS_packages}" ]; then
can't you just -z "${PACKAGE_LIST}" here?

[sosa, 2010-11-22 21:23:31]

Talked offline about this but our resolution was not to use -z because we don't
want the pfq to specify no packages but for the unit test script to interpret
this as meaning to rev all.