HADOOP-15283. Upgrade from findbugs 3.0.1 to spotbugs 3.1.2 in branch-2 to fix docker image build.

(cherry picked from commit 8ad3ec6aabd265cae01242100729e3d02d794256)

dev-support/docker/Dockerfile

@@ -84,14 +84,15 @@ RUN apt-get -q update
 RUN apt-get -q install --no-install-recommends -y openjdk-7-jdk
 
 ######
-# Install findbugs
+# Install spotbugs (successor of findbugs)
 ######
-RUN mkdir -p /opt/findbugs && \
+RUN mkdir -p /opt/spotbugs && \
     curl -L -s -S \
-         https://sourceforge.net/projects/findbugs/files/findbugs/3.0.1/findbugs-noUpdateChecks-3.0.1.tar.gz/download \
-         -o /opt/findbugs.tar.gz && \
-    tar xzf /opt/findbugs.tar.gz --strip-components 1 -C /opt/findbugs
-ENV FINDBUGS_HOME /opt/findbugs
+         http://repo.maven.apache.org/maven2/com/github/spotbugs/spotbugs/3.1.2/spotbugs-3.1.2.tgz \
+         -o /opt/spotbugs.tar.gz && \
+    tar xzf /opt/spotbugs.tar.gz --strip-components 1 -C /opt/spotbugs
+# Hadoop uses FINDBUGS_HOME to run spotbugs
+ENV FINDBUGS_HOME /opt/spotbugs
 
 ####
 # Install shellcheck