Fix CI script for running simulator in background

Don't hardcode bin path inside the tox env (should be on the PATH), also
check early if the process died for some reason.

ci/run-with-sim.sh

@@ -4,10 +4,10 @@
 
 set -eu
 
-.tox/notebooks/bin/libertem-live-mib-sim --host 127.0.0.1 "$TESTDATA_BASE_PATH/20200518 165148/default.hdr" --cached=MEMFD --wait-trigger&
+libertem-live-mib-sim --host 127.0.0.1 "$TESTDATA_BASE_PATH/20200518 165148/default.hdr" --cached=MEMFD --wait-trigger&
 MERLIN_SIM_PID=$!
 
-.tox/notebooks/bin/libertem-live-dectris-sim "$TESTDATA_BASE_PATH/dectris/zmqdump.dat.128x128-id34-exte-bslz4" --port 8910 --zmqport 9999&
+libertem-live-dectris-sim "$TESTDATA_BASE_PATH/dectris/zmqdump.dat.128x128-id34-exte-bslz4" --port 8910 --zmqport 9999&
 DECTRIS_SIM_PID=$!
 
 cleanup() {
@@ -20,6 +20,20 @@ cleanup() {
 
 trap cleanup EXIT
 
+sleep 1
+
+# check if the subprocesses failed already:
+
+if ! test -d /proc/"$MERLIN_SIM_PID"/; then
+    echo "merlin sim failed to start"
+    exit 1
+fi
+
+if ! test -d /proc/"$DECTRIS_SIM_PID"/; then
+    echo "dectris sim failed to start"
+    exit 1
+fi
+
 echo "started merlin simulator in background, pid=$MERLIN_SIM_PID"
 echo "started dectris simulator in background, pid=$DECTRIS_SIM_PID"
 echo "waiting for data sockets to be ready..."