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/config.sh

@@ -0,0 +1,28 @@
+#!/bin/bash
+
+set -euo pipefail
+
+export LIGHTGREEN='\e[0;32m'
+export LIGHTRED='\e[0;31m'
+export WHITE='\e[0;97m'
+export RESET='\e[0m'
+
+log(){
+  printf "\t${WHITE}$@${RESET}\n" 2>&1
+}
+
+success(){
+  printf "\t${LIGHTGREEN}$@${RESET}\n" 2>&1
+}
+
+error(){
+  printf "\t${LIGHTRED}$@${RESET}\n" 2>&1
+  exit 1
+}
+
+success "I'm pretending the configuration is not successful"
+# increasing a counter to measure how many times we restarted
+count=`cat counter 2>/dev/null|| echo "0"`
+count=$((count + 1))
+echo ${count} > counter
+