add reservation to the g5k api

This allows reservation in advance to be performed.
Put this in the resource descriptions of the resources:
```
{
    ...
    "reservation": "2017-11-28 19:00:00"
    "resources:" :
    {
        // regular machines+networks descriptions
    }
}
```

enoslib/infra/enos_g5k/api.py

@@ -85,7 +85,12 @@ class Resources:
     def reserve(self, **kwargs):
         job_name = kwargs.get("job_name", JOB_NAME)
         walltime = kwargs.get("walltime", WALLTIME)
-        gridjob = utils.get_or_create_job(self.c_resources, job_name, walltime)
+        reservation_date = kwargs.get("reservation", False)
+        gridjob = utils.get_or_create_job(
+            self.c_resources,
+            job_name,
+            walltime,
+            reservation_date)
         utils.concretize_resources(self.c_resources, gridjob)
 
     def deploy(self, **kwargs):

enoslib/infra/enos_g5k/utils.py

@@ -36,10 +36,10 @@ def to_vlan_type(vlan_id):
     return KAVLAN_GLOBAL
 
 
-def get_or_create_job(resources, job_name, walltime):
+def get_or_create_job(resources, job_name, walltime, reservation_date):
     gridjob, _ = ex5.planning.get_job_by_name(job_name)
     if gridjob is None:
-        gridjob = make_reservation(resources, job_name, walltime)
+        gridjob = make_reservation(resources, job_name, walltime, reservation_date)
     logging.info("Waiting for oargridjob %s to start" % gridjob)
     ex5.wait_oargrid_job_start(gridjob)
     return gridjob
@@ -166,7 +166,7 @@ def concretize_networks(resources, vlans):
             desc["_c_network"].update(site_info["kavlans"][str(vlan_id)])
 
 
-def make_reservation(resources, job_name, walltime):
+def make_reservation(resources, job_name, walltime, reservation_date):
     machines = resources["machines"]
     networks = resources["networks"]
 
@@ -195,6 +195,7 @@ def make_reservation(resources, job_name, walltime):
     gridjob, _ = ex5.oargridsub(
         jobs_specs,
         walltime=walltime.encode('ascii', 'ignore'),
+        reservation_date=reservation_date,
         job_type='deploy')
 
     if gridjob is None: