Use exec instead of bash to start java

Fix passing multiple arguments
Add test for jenkins arguments and JENKINS_OPTS
diff --git a/jenkins.sh b/jenkins.sh
index d943ffc..dd28123 100755
--- a/jenkins.sh
+++ b/jenkins.sh
@@ -29,7 +29,7 @@
 
 # if `docker run` first argument start with `--` the user is passing jenkins launcher arguments
 if [[ $# -lt 1 ]] || [[ "$1" == "--"* ]]; then
-  exec /bin/bash -c "java $JAVA_OPTS -jar /usr/share/jenkins/jenkins.war $JENKINS_OPTS $@"
+  exec java $JAVA_OPTS -jar /usr/share/jenkins/jenkins.war $JENKINS_OPTS "$@"
 fi
 
 # As argument is not jenkins, assume user want to run his own process, for sample a `bash` shell to explore this image