bugzilla-create: take bugzilla email from BUGZILLA_ACCOUNT_EMAIL env var
Some people have emails in bugzilla that are completely different than
emails they use in git and providing one with -e option is tedious.
Make bugzilla-create more flexible by providing the third options that
sits between command line option and git-config automation.
Signed-off-by: Miroslav Franc <mfranc@suse.cz>