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/should_retry_configuring/test.sh

@@ -0,0 +1,74 @@
+#!/bin/bash
+
+# UNITTEST: retry config
+# Will simulate a configuration failure and expects:
+# - the configuration step to be run 10 times
+# - the entrypoint script to exit with error code 2
+# - the runsvc.sh script to never run.
+
+source ../logging.sh
+
+entrypoint_log() {
+  while read I; do
+    printf "\tentrypoint.sh: $I\n"
+  done
+}
+
+log "Setting up the test"
+export UNITTEST=true
+export RUNNER_HOME=localhome
+export RUNNER_NAME="example_runner_name"
+export RUNNER_REPO="myorg/myrepo"
+export RUNNER_TOKEN="xxxxxxxxxxxxx"
+
+mkdir -p ${RUNNER_HOME}/bin
+# add up the config.sh and runsvc.sh
+ln -s ../config.sh ${RUNNER_HOME}/config.sh
+ln -s ../../runsvc.sh ${RUNNER_HOME}/bin/runsvc.sh
+
+cleanup() {
+  rm -rf ${RUNNER_HOME}
+  unset UNITTEST
+  unset RUNNERHOME
+  unset RUNNER_NAME
+  unset RUNNER_REPO
+  unset RUNNER_TOKEN
+}
+
+trap cleanup SIGINT SIGTERM SIGQUIT EXIT
+
+log "Running the entrypoint"
+log ""
+
+../../../runner/entrypoint.sh 2> >(entrypoint_log)
+
+if [ "$?" != "2" ]; then
+  error "========================================="
+  error "Configuration should have thrown an error"
+  exit 1
+fi
+success "Entrypoint didn't complete successfully"
+success ""
+
+log "Checking the counter, should have 10 iterations"
+count=`cat ${RUNNER_HOME}/counter || "notfound"`
+if [ "${count}" != "10" ]; then
+  error "============================================="
+  error "The retry loop should have done 10 iterations"
+  exit 1
+fi
+success "Retry loop went up to 10"
+success
+
+log "Checking that runsvc never ran"
+if [ -f ${RUNNER_HOME}/runsvc_ran ]; then
+  error "================================================================="
+  error "runsvc was invoked, entrypoint.sh should have failed before that."
+  exit 1
+fi
+
+success "runsvc.sh never ran"
+success
+success "==========================="
+success "Test completed successfully"
+exit 0