alarms: decorate data source to capture connector errors as alarms

This patch converts the alarm definitions which filter
database connection failures by creating a wrapper/decorator
class which logs these as Alarm types, and by substituting
the decorator class for its delegate classes in the
object field types and spring injection files.

It could be argued that a more elegant solution would
have been to do this using aspect (a natural fit), but
my experience with AspectJ is limited (coding examples
written during a workshop class), so I adopted this
approach as the shorter/quicker path.

Target: master
Patch: https://rb.dcache.org/r/7138/
Require-notes: yes
Require-book: no
Acked-by: Dmitry

RELEASE NOTES

Note: this patch ought to be applied together with 7137.
Since it falls under the general category of those
changes, no special notice need be given on the release notes.