Fork a package using anonymous auth
    
    When the repo is cloned anonymously (`fedpkg clone -a`), `fork`
    should work in the 'anonymous' mode as well. Fork API call
    is the same, but the added remote has a different address = https
    protocol instead of ssh.
    Fedpkg detects whether `fork` is executed upon an anonymous repo.
    The User can force anonymous mode using (`fedpkg fork -a`) parameter.
    
    Fixes: #574
    JIRA: RHELCMP-14205
    
    Signed-off-by: Ondřej Nosek <onosek@redhat.com>