Quickstart.sh should require JAVA_HOME is set

No way to tell that the pillars failed to start due to not having set JAVA_HOME

abr@pc596:~/dockers/bitrepository-quickstart$ export JAVA_HOME=""
abr@pc596:~/dockers/bitrepository-quickstart$ ./quickstart.sh start
Using CATALINA_BASE: /home/abr/dockers/bitrepository-quickstart/tomcat
Using CATALINA_HOME: /home/abr/dockers/bitrepository-quickstart/tomcat
Using CATALINA_TMPDIR: /home/abr/dockers/bitrepository-quickstart/tomcat/temp
Using JRE_HOME: /usr
Using CLASSPATH: /home/abr/dockers/bitrepository-quickstart/tomcat/bin/bootstrap.jar:/home/abr/dockers/bitrepository-quickstart/tomcat/bin/tomcat-juli.jar
Using CATALINA_PID: /home/abr/dockers/bitrepository-quickstart/tomcat/pid.tomcat
Tomcat started.