Adding some unit testing for entrypoint.sh

The unit tests are simulating a run for entrypoint. It creates some
dummy config.sh and runsvc.sh and makes sure the logic behind
entrypoint.sh is correct.

Unfortunately the entrypoint.sh contains some sections that are not
mockable so I had to put some logic in there too.

Testing includes for now:
- the normal scenario
- the normal non-ephemeral scenario
- the configuration failure scenario

Also tested the entrypoint.sh on a real runner, still works as expected.

test/entrypoint/entrypoint_unittest.sh

@@ -0,0 +1,37 @@
+#!/bin/bash
+
+source logging.sh
+
+for unittest in ./should*; do
+  log "**********************************"
+  log " UNIT TEST: ${unittest}"
+  log "**********************************"
+  log ""
+
+  cd ${unittest}
+  ./test.sh
+  ret_code=$?
+  cd ..
+
+  log ""
+  log ""
+  if [ "${ret_code}" = "0" ]; then
+    success "Completed: unit test ${unittest}"
+  else
+    error "Completed: unit test ${unittest} with errors"
+    failed="true"
+  fi
+done
+
+if [ -n "${failed:-}" ]; then
+  error ""
+  error "*************************************"
+  error "All unit tests completed, with errors"
+  error "*************************************"
+  exit 1
+else
+  success ""
+  success "***************************************"
+  success "All unit tests completed with no errors"
+  success "***************************************"
+fi