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>