cosmetic: gerrit: use variables for the files to patch

Make the code more readable, and make it easier to update the paths
if they should change again.

Change-Id: I285f7908de64f2d92fa99ae9d74fb2e29ec72771

gerrit/Dockerfile

@@ -3,16 +3,21 @@ FROM gerritcodereview/gerrit
 USER root
 RUN yum -y install zip unzip patch
 
+# Patch LoginForm.html (unpack and repack from gerrit.war)
+ARG gerritwar="/var/gerrit/bin/gerrit.war"
+ARG libopenid="WEB-INF/lib/com_google_gerrit_httpd_auth_openid_libopenid.jar"
+ARG loginform="com/google/gerrit/httpd/auth/openid/LoginForm.html"
+
 RUN \
-	unzip /var/gerrit/bin/gerrit.war WEB-INF/lib/com_google_gerrit_httpd_auth_openid_libopenid.jar && \
-	unzip WEB-INF/lib/com_google_gerrit_httpd_auth_openid_libopenid.jar com/google/gerrit/httpd/auth/openid/LoginForm.html
+	unzip "$gerritwar" "$libopenid" && \
+	unzip "$libopenid" "$loginform"
 
 COPY add_osmocom.diff /tmp
 RUN patch -p0 < /tmp/add_osmocom.diff
 
 RUN \
-	zip -u WEB-INF/lib/com_google_gerrit_httpd_auth_openid_libopenid.jar com/google/gerrit/httpd/auth/openid/LoginForm.html && \
-	zip -u /var/gerrit/bin/gerrit.war WEB-INF/lib/com_google_gerrit_httpd_auth_openid_libopenid.jar
+	zip -u "$libopenid" "$loginform" && \
+	zip -u "$gerritwar" "$libopenid"
 
 USER gerrit