Log cms_verify issues as warnings (not errors).

In general we probably do want to log these types of errors... but
not as ERRORS. I think log Warning messages are probably more
appropriate here since it would be possible to hit this when
expired certs are refreshed...

Fixes LP Bug #1190230.

Change-Id: I0383f7e490ddcdfb31a62cd3760102152a8d16d9
Merge "Log cms_verify issues as warnings (not errors)."