Bug 1391476 - Don't install nexus.xml in a Docker volume; r=mshal

We're about to ban files in Docker volumes so they behave almost
identically to caches (which start empty).

We move the install of nexus.xml from Docker image time to
task time. This also means that changes to nexus.xml don't result
in having to rebuild the Docker image.

MozReview-Commit-ID: JIjeJN4mt2

--HG--
rename : taskcluster/docker/android-gradle-build/nexus.xml => taskcluster/scripts/builder/build-android-dependencies/nexus.xml
extra : rebase_source : 53848f06820bda7979b2ae15456e07f8aed2363d

taskcluster/docker/android-gradle-build/Dockerfile

@@ -113,8 +113,6 @@ RUN tar zxf nexus-${NEXUS_VERSION}-bundle.tar.gz \
 # So that we don't have to RUN_AS_USER=root.
 RUN chown -R worker:worker /opt/sonatype/nexus/
 
-COPY nexus.xml /home/worker/workspace/nexus/conf/nexus.xml
-
 # Back to the centos6-build workdir, matching desktop-build.
 WORKDIR /home/worker
 

taskcluster/scripts/builder/build-android-dependencies/before.sh

@@ -8,6 +8,9 @@ echo "running as" $(id)
 
 set -v
 
+mkdir -p ${WORKSPACE}/nexus/conf
+cp /home/worker/workspace/build/src/taskcluster/scripts/builder/build-android-dependencies/nexus.xml ${WORKSPACE}/nexus/conf/nexus.xml
+
 # Populate /home/worker/workspace/build/src/java_home.
 . $WORKSPACE/build/src/taskcluster/scripts/builder/build-android-dependencies/repackage-jdk-centos.sh