jenkins-build-makebuildserver: add rudimentary rewritemeta test

This will show if rewritemeta changed anything.  fdroiddata requires all
files to be rewritten with rewritemeta before they are accepted.

jenkins-build-makebuildserver

@@ -97,3 +97,6 @@ test -d archive || mkdir archive
 ../fdroid gpgsign --verbose
 ../fdroid update --verbose --nosign
 ../fdroid signindex --verbose
+
+../fdroid rewritemeta --verbose
+git --no-pager diff