mysql: Retry connecting to mysql.

Retry connecting to mysql on OperationalError exception.

BUG=chromium:478919
TEST=Ran the smoke suite on moblab. Ran unit tests.

Change-Id: I86b664e7d3c4ab5ec46eacddee24dd3fa671b996
Reviewed-on: https://chromium-review.googlesource.com/266596
Tested-by: Gabe Black <gabeblack@chromium.org>
Commit-Queue: Gabe Black <gabeblack@chromium.org>
Trybot-Ready: Gabe Black <gabeblack@chromium.org>
Reviewed-by: Dan Shi <dshi@chromium.org>
1 file changed