Optionally give mysql user all global privs.

One our single use unittest slaves we want to allow unittests to create
and destroy arbitrary mysql database schemas. The simplest way to do
this is to grant all priveleges to the test user on the mysql server
globally. This is safe because the nodes are thrown away post test.

Change-Id: Ic92ff2f9c752d955e6f82eb4b88330b5448cfa75
Merge "Optionally give mysql user all global privs."