support link-local IPv6 host addresses

SSHing to a link-local IPv6 address requires the following syntax:
   
    ssh fe80::74f8:52ff:fe00:4%eth1

This change adds "%interface" as part of IPv6 host regex in fabric.

    [fe80::74f8:52ff:fe00:4%eth1] Executing task 'foo'
    [fe80::74f8:52ff:fe00:4%eth1] put: test1.txt -> /tmp/test1.txt