Add reservation option.

Author: Gwen

batchspawner/batchspawner.py

@@ -513,6 +513,10 @@ class SlurmSpawner(UserEnvMixin,BatchSpawnerRegexStates):
         help="QoS name to submit job to resource manager"
         ).tag(config=True)
 
+   req_reservation = Unicode('', \
+        help="Reservation name to submit to resource manager"
+        ).tag(config=True)
+
     batch_script = Unicode("""#!/bin/bash
 #SBATCH --output={{homedir}}/jupyterhub_slurmspawner_%j.log
 #SBATCH --job-name=spawner-jupyterhub