Add fingerprint for bug 1403284

Starting to see mysql complain about 'Too many connections' during
large-ops testing.

67 hits in past 10 days (some duplicates since see multiple stacktraces
per job), all failures.

Change-Id: Icbbf155c610ed11e76daf64b3300b186d55dcc0b
Related-Bug: 1403284
Merge "Add fingerprint for bug 1403284"