fix(google-daemon): use * for the passwd not !

useradd defaults to using ! as the "locked" password marker.
Unfortunatly, openssh interprets this to mean that it shouldn't let the
user in via ssh if PAM is missing. Work around this by using the *
marker which also means locked but is allowed by openssh.
Merge pull request #55 from coreos/master

fix(google-daemon): use * for the passwd not !