perforce-sdp-install: copy configurables.cfg into /p4/common/config after mkdirs
mkdirs.sh renders the per-instance config files but does not copy the SDP
configurables.cfg into the deployed /p4/common/config. ccheck.sh (invoked by
configure_new_server.sh) loads its [prod] profile from that path, so a new
install would fail configure_new_server until the file is placed by hand.