s4 messaging tests: Fix race condition in smbcontrol tests

s4 messaging tests: Fix race condition in smbcontrol tests

The test for the smbcontrol sleep command and the inject fault command
both used the "rpc_server" process as a target.  As the inject fault
command caused the process to restart there was a race condition between
the process restarting and the sleep test running.  To prevent this the
tests now use different target processes.

Signed-off-by: Gary Lockyer <gary@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>
Autobuild-User(master): Andrew Bartlett <abartlet@samba.org>
Autobuild-Date(master): Fri Dec 21 03:39:24 CET 2018 on sn-devel-144