Turns out I wasted a couple of hours discovering that Stash 2.10.1 only works with a back-revved version of the MySQL Connector (mysql-connector-java-5.1.10.jar) while the version include with EL 6.4:

root@ma-gncspsd-lapp44:/ngs/app/stash# rpm -q mysql-connector-java
mysql-connector-java-5.1.17-6.el6.noarch

... causes this error on startup:

org.springframework.jdbc.CannotGetJdbcConnectionException: Could not get JDBC Connection; nested exception is com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: Could not create connection to database server. Attempted reconnect 3 times. Giving up.