Bug 28017: Allow non-FQDN (@localhost) addresses

Bug 28017: Allow non-FQDN (@localhost) addresses

This patch makes Koha::Email support using @localhost addresses.

To test:
1. Apply the regression tests
2. Run:
   $ kshell
  k$ prove t/Koha/Email.t
=> FAIL: Koha::Email doesn't support non-fqdn addresses
3. Apply this patch
4. Repeat 2
=> SUCCESS: All tests pass!
5. Sign off :-D

Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>