ATS-400 : Build improvements for TravisCI (#24)

* ATS-400 : Build improvements for TravisCI

Building the LibreOffice docker image takes a long time due to the
large packages that need to be downloaded and installed. This results
in more than 10 minutes of inactivity in the build log and TravisCI
kills the job.
Improvements:
- remove and replace unnecessary steps in Docker builds
- cache LibreOffice GZIP distribution in Travis

_ci/cache_artifacts.sh

@@ -0,0 +1,22 @@
+#!/usr/bin/env bash
+
+echo "=========================== Starting Cache Artifacts Script ==========================="
+PS4="\[\e[35m\]+ \[\e[m\]"
+set -vex
+pushd "$(dirname "${BASH_SOURCE[0]}")/../"
+
+# Cache the LibreOffice distribution, as it is takes a long time to download and it can cause the
+# build to fail (no output for more than 10 minutes)
+LIBREOFFICE_RPM_URL="https://nexus.alfresco.com/nexus/service/local/repositories/thirdparty/content/org/libreoffice/libreoffice-dist/5.4.6/libreoffice-dist-5.4.6-linux.gz"
+if [ -f "${HOME}/artifacts/libreoffice-dist-5.4.6-linux.gz" ]; then
+    echo "Using cached LibreOffice distribution..."
+else
+    echo "Downloading LibreOffice distribution..."
+    curl -s -S ${LIBREOFFICE_RPM_URL} -o "${HOME}/artifacts/libreoffice-dist-5.4.6-linux.gz"
+fi
+cp "${HOME}/artifacts/libreoffice-dist-5.4.6-linux.gz" alfresco-docker-libreoffice/
+
+
+popd
+set +vex
+echo "=========================== Finishing Cache Artifacts Script =========================="