Remove shibboleth2.xml configuration file before volume declaration

Edit Dockerfile for the I2 image so that the shibboleth2.xml file
installed by the Shibboleth SP RPM is removed and not present when the
VOLUME is declared. This is necessary so that if the deployer does not
mount in a shibboleth2.xml and instead uses environment variables to
inject configuration details the entrypoint script creates the
shibboleth2.xml file dynamically.

comanage-match-internet2-tap/Dockerfile

@@ -104,7 +104,8 @@ RUN cd /etc/httpd/conf.d \
     && cd /var/www/html \
     && ln -s ${COMANAGE_MATCH_DIR}/app/webroot match \
     && rm -rf ${COMANAGE_MATCH_DIR}/local/* \
-    && chown -R apache:apache ${COMANAGE_MATCH_DIR}/app/tmp
+    && chown -R apache:apache ${COMANAGE_MATCH_DIR}/app/tmp \
+    && rm -f /etc/shibboleth/shibboleth2.xml
 
 # Allow value for first administrator bootstrapped into the
 # platform to be specified at image build time, in addition to