remove "No hosts matched" from --list-hosts

Ansible --list-hosts says "No hosts matched" on stdout when it matches
no hosts.  Emitting "No hosts matched" on stdout interferes with a
script doing something useful with the lack of matching hosts.

    % ansible -i hosts --list-hosts fred
    No hosts matched
    % ansible -i hosts --list-hosts fred >/dev/null
    % for h in $( ansible -i hosts --list-hosts fred ) ; do echo $h ; done
    No
    hosts
    matched
    % ansible --version
    ansible 1.5.3

My preference is to simply emit nothing in this case, not even on
stderr.  That no hosts were matched is evident from the lack of
hosts emitted.

Note that this behavior is new in 1.5.  It didn't do this in 1.4.3.