abdt_logging: log more detail on_retry_exception

Show more context and the traceback when logging a call to
on_retry_exception().

Test Plan:
$ ./precommit.sh
$ ./testbed/arcyd/unreliable_git_loop_test.sh
    .. wait long enough for an error to occur ..
    .. stop loop and examine var/log/info for details ..
Arcyd: log errors when reporting exceptions

Update the existing messaging exception handler to also log errors when
reporting.

Test Plan:
Just in case I missed something
$ ./precommit.sh

Exercise the changed code directly with
.. change bad_git_push_arcyd.py to fail all fetches ..
$ ./testbed/arcyd/unreliable_git_loop_test.sh
    .. wait long enough for fetch fail to escalate to handler ..
    .. stop and examine log output to make sure is as expected ..