test: allow specifying RUN_NIGHTLY from command line

This can be useful when running nightly tests locally.

Signed-off-by: Jim Harris <james.r.harris@intel.com>
Change-Id: I54d375f9e8d13d8c6dcdac3d81bbf9dc1fcd77f0

Reviewed-on: https://review.gerrithub.io/393681
Reviewed-by: Daniel Verkamp <daniel.verkamp@intel.com>
Tested-by: SPDK Automated Test System <sys_sgsw@intel.com>
Reviewed-by: Ben Walker <benjamin.walker@intel.com>

scripts/autotest_common.sh

@@ -9,7 +9,8 @@ set -e
 PS4=' \t	\$ '
 ulimit -c unlimited
 
-export RUN_NIGHTLY=0
+: ${RUN_NIGHTLY:=0}
+export RUN_NIGHTLY
 
 if [[ ! -z $1 ]]; then
 	if [ -f $1 ]; then