Save sources in a mirror and cache it in Travis (#7392)

share/spack/qa/run-build-tests

@@ -11,6 +11,12 @@
 . "$(dirname $0)/setup.sh"
 check_dependencies ${coverage} git hg svn
 
+# Fetch the sources in a mirror, and add it to Spack
+mkdir -p ~/.mirror
+bin/spack mirror add travis ~/.mirror
+bin/spack mirror create -D -d ~/.mirror ${SPEC}
+
+
 # Move to root directory of Spack
 # Allows script to be run from anywhere
 cd "$SPACK_ROOT"