Minor Docker cleanups

* Fix typo in `COPY` command
* Update `JENKINS_VERSION` to match actual version downloaded
* Add `-f` to Curl call to fail on HTTP codes >= 400
* Add `set -e` to entrypoint script to fail on errors
* Change `echo` commands in entrypoint to echo to STDERR
* Make entrypoint whitespace consistent
diff --git a/Dockerfile b/Dockerfile
index 6a23b35..71c3430 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -26,7 +26,7 @@
 
 # could use ADD but this one does not check Last-Modified header 
 # see https://github.com/docker/docker/issues/8331
-RUN curl -L http://mirrors.jenkins-ci.org/war-stable/$JENKINS_VERSION/jenkins.war -o /usr/share/jenkins/jenkins.war \
+RUN curl -fL http://mirrors.jenkins-ci.org/war-stable/$JENKINS_VERSION/jenkins.war -o /usr/share/jenkins/jenkins.war \
   && echo "$JENKINS_SHA /usr/share/jenkins/jenkins.war" | sha1sum -c -
 
 ENV JENKINS_UC https://updates.jenkins-ci.org