jenkins: add --enable-external-tests

Run the new logging_vty_test.vty VTY transcript test in our CI.

Change-Id: Ic4ec1f6c131da50b3956f16f0b49375f387196b3
diff --git a/contrib/jenkins_arm.sh b/contrib/jenkins_arm.sh
index 1d72f2f..e3a6cd1 100755
--- a/contrib/jenkins_arm.sh
+++ b/contrib/jenkins_arm.sh
@@ -18,6 +18,7 @@
 	--enable-embedded \
 	--disable-doxygen \
 	--disable-shared \
+	--enable-external-tests \
 	CFLAGS="-Os -ffunction-sections -fdata-sections -nostartfiles -nodefaultlibs $WERROR_FLAGS"
 
     $MAKE $PARALLEL_MAKE