test-webservice: Avoid leaking mock-sshd processes

With Linux PR_SET_PDEATHSIG, if the test program dies, that will
automatically terminate the child.  To make this work, we also need to
tell GLib not to double-fork, so it remains our child and not pid 1's.
test-webservice: Explicitly use 127.0.0.1

mock-sshd doesn't listen on IPV6, but GSocketClient will resolve
"localhost" to that on RHEL7 at least.
wip