Tighten ERROR regexp in log checker

Because each project uses a slightly different format for logging, and
sometimes different formats within a project, it is hard to match ERROR as
the log level across all log files. There was a failure caused by "ERROR"
actually showing up inside a keystone token. This change will prevent that
though it is still possible something else could slip through.

Change-Id: Ic8b036b4ed7481856231b2d073d273b1df783415
Merge "Tighten ERROR regexp in log checker"