MySQL table_open_cache size unusually small

https://bugzilla.redhat.com/show_bug.cgi?id=1080547 Users do not have the
ability to change table_open_cache to values other than 4 (and have them
stick).  The set value seems too low to allow database operations to remain
efficient.  For example, in my app I have 18 tables that are constantly being
written to from a single persistent connection, but can only have four tables
cached at a time.  This leads to tables having to be re-opened which causes
fairly significant disk I/O.