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

alfresco-docker-libreoffice/Dockerfile

@@ -15,17 +15,17 @@ ARG GROUPID=1000
 ARG USERNAME=libreoffice
 ARG USERID=33003
 
-COPY target/alfresco-docker-libreoffice-${env.project_version}.jar /usr/bin
+COPY target/alfresco-docker-libreoffice-${env.project_version}.jar libreoffice-dist-*-linux.gz /
 
-RUN ln /usr/bin/alfresco-docker-libreoffice-${env.project_version}.jar /usr/bin/alfresco-docker-libreoffice.jar && \
-    yum install -y wget && \
+RUN ln /alfresco-docker-libreoffice-${env.project_version}.jar /usr/bin/alfresco-docker-libreoffice.jar && \
     yum install -y cairo cups-libs libSM && \
-    wget $LIBREOFFICE_RPM_URL && \
-    wget $LIBREOFFICE_LICENSE_FILE && \
-    tar xzf libreoffice-dist-*-linux.gz && \
+    test -f libreoffice-dist-5.4.6-linux.gz && \
+    mv libreoffice-dist-5.4.6-linux.gz libreoffice-dist-linux.gz || \
+    curl -s -S $LIBREOFFICE_RPM_URL      -o libreoffice-dist-linux.gz && \
+    curl -s -S $LIBREOFFICE_LICENSE_FILE -o libreoffice.txt && \
+    tar xzf libreoffice-dist-linux.gz && \
     yum localinstall -y LibreOffice*/RPMS/*.rpm && \
-    rm -rf libreoffice-dist-*-linux.gz LibreOffice_*_Linux_x86-64_rpm && \
-    yum remove -y wget && \
+    rm -rf libreoffice-dist-linux.gz LibreOffice_*_Linux_x86-64_rpm && \
     yum clean all
 
 ADD target/generated-resources/licenses              /licenses

alfresco-docker-libreoffice/pom.xml

@@ -75,7 +75,6 @@
                 <groupId>io.fabric8</groupId>
                 <artifactId>fabric8-maven-plugin</artifactId>
                 <configuration>
-                    <verbose/>
                     <images>
                         <image>
                             <name>${image.name}:${image.tag}</name>
@@ -120,7 +119,6 @@
                         <groupId>io.fabric8</groupId>
                         <artifactId>fabric8-maven-plugin</artifactId>
                         <configuration>
-                            <verbose/>
                             <images>
                                 <!-- QuayIO image -->
                                 <image>
@@ -162,7 +160,6 @@
                         <groupId>io.fabric8</groupId>
                         <artifactId>fabric8-maven-plugin</artifactId>
                         <configuration combine.self="override">
-                            <verbose/>
                             <images>
                                 <!-- QuayIO image -->
                                 <image>