[autotest] Set rpm info cache expriation to 30 mins.

Set rpm info cache expriation to 30 mins.
Any changes to rpm attributes in db will eventually picked up
by rpm after 30 mins.

BUG=chromium:517233
TEST=Unittest.
DEPLOY=rpm

Change-Id: I860933cd774a005dc27daf2bbb511b2f3672e049
Reviewed-on: https://chromium-review.googlesource.com/305370
Commit-Ready: Fang Deng <fdeng@chromium.org>
Tested-by: Fang Deng <fdeng@chromium.org>
Reviewed-by: Paul Hobbs <phobbs@google.com>
2 files changed