remote: change socket helper to return full daemon path

remote: change socket helper to return full daemon path

The remoteGetUNIXSocket method currently just returns the daemon name
and the caller then converts this to a path. Except the SSH helper
didn't do this, so it was relying on later code expanding $PATH, and
this doesn't allow for build root overrides.

Reviewed-by: Ján Tomko <jtomko@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>