examples.wrappers.rr: Support spaces in output dir

The path variables need to be quotated.
Signed-off-by: NLukáš Doktor <ldoktor@redhat.com>

examples/wrappers/rr.sh

@@ -3,7 +3,7 @@
 # Record deterministic execution using rr (http://rr-project.org)
 #
 
-export _RR_TRACE_DIR=$AVOCADO_TEST_OUTPUTDIR/rr
-mkdir -p $_RR_TRACE_DIR
+export _RR_TRACE_DIR="$AVOCADO_TEST_OUTPUTDIR/rr"
+mkdir -p "$_RR_TRACE_DIR"
 exec rr record -n "$@"