Bug 1326205: Error installing triggers for new mahara site in MySQL with dbprefix

MySql has a maximum of 64 characters for identifiers.
Shorten the names of the triggers to allow space for dbprefix and the '_trigger' suffix.
Apply the name change to both postgres and mysql to keep names aligned.

Change-Id: I729a5e5f4dd8b33dba1aa3f8ddeae92457c50c27
Signed-off-by: Ghada El-Zoghbi <ghada@catalyst-au.net>
Merge "Bug 1326205: Error installing triggers for new mahara site in MySQL with dbprefix"