dist: recognize epel-7-x86_64 mock target and enable networking

The default epel-7-x86_64 wisely disables networking, however our
maven build accesses the maven repository during the build process.

Recognize the target name and redirect it to our networking-enabled
configuration.

Message-Id: <20180408122138.16672-1-avi@scylladb.com>

dist/redhat/build_rpm.sh

@@ -52,6 +52,10 @@ if [ -z "$TARGET" ]; then
     fi
 fi
 
+if [[ "$TARGET" = epel-7-x86_64 ]]; then
+    TARGET=./dist/redhat/mock/scylla-jmx-epel-7-x86_64.cfg
+fi
+
 if [ ! -f /usr/bin/mock ]; then
     pkg_install mock
 fi