Add irc_timezone to testing.yml to fix dev build

Vagrant provisioning currently fails without irc_timezone set in
vars/testing.yml.  This is probably due to changes introduced in
al3x/sovereign#300 to permit the znc timezone to be configured.  The
file vars/users.yml already has a TODO entry for irc_timezone.
Merge pull request #302 from cthachuk/fix-testing-cfg

Merge pull request #302