Change server exceptions to show less details

Internal exceptions were dumping error messages raised by
arbitrary python calls and potentially revealing sensitive
details.

The message for all 500 errors is now::

    Internal Server Error. (<UUID>)

The original exception details are written to the log files. The
UUID can be used to reference the individual 500 error in the log.

Change-Id: I57e13a182fd868a1f45419b51d08fe744d650e5f
Fixes: bug #1189673
Merge "Change server exceptions to show less details"