`toil clean` doesn't clean up job stores on Azure
I've been running jobs with Azure job stores, and I've been wanting to restart them from scratch. I'm supposed to be able to do this with `toil clean`, but it doesn't work.

```
anovak@amn2master1:~/hgvm-graph-bakeoff-evaluations$ toil clean azure:hgvm:amntree
amn2master1 2016-08-29 20:12:58,971 MainThread INFO toil.lib.bioio: Logging set at level: INFO
amn2master1 2016-08-29 20:12:58,971 MainThread INFO toil.utils.toilClean: Attempting to delete the job store
amn2master1 2016-08-29 20:12:59,034 MainThread INFO toil.utils.toilClean: Successfully deleted the job store
anovak@amn2master1:~/hgvm-graph-bakeoff-evaluations$ scripts/parallelMappingEvaluation.py azure:hgvm:amntree graph_urls.tsv azure:hgvm:pilot-input/reads azure:hgvm:pilot-output/low-coverage/aug16/out1 --batchSystem=mesos --mesosMaster 10.0.0.5:5050 --kmer_size=16 --edge_max=3 --index_mode gcsa-mem --include_primary --sample_limit 10 --disableCaching --workDir /tmp 2>&1 | tee log.txt
INFO:toil.lib.bioio:Logging set at level: INFO
INFO:toil.lib.bioio:Logging set at level: INFO
INFO:requests.packages.urllib3.connectionpool:Starting new HTTPS connection (1): hgvm.table.core.windows.net
Traceback (most recent call last):
  File "scripts/parallelMappingEvaluation.py", line 1170, in <module>
    sys.exit(main(sys.argv))
  File "scripts/parallelMappingEvaluation.py", line 1160, in main
    failed_jobs = Job.Runner.startToil(root_job,  options)
  File "/usr/local/lib/python2.7/dist-packages/toil/job.py", line 540, in startToil
    with Toil(options) as toil:
  File "/usr/local/lib/python2.7/dist-packages/toil/common.py", line 501, in __enter__
    jobStore.initialize(config)
  File "/usr/local/lib/python2.7/dist-packages/toil/jobStores/azureJobStore.py", line 152, in initialize
    raise JobStoreExistsException(self.locator)
toil.jobStores.abstractJobStore.JobStoreExistsException: The job store 'hgvm:amntree' already exists. Use --restart to resume the workflow, or remove the job store with 'toil clean' to start the workflow from scratch
anovak@amn2master1:~/hgvm-graph-bakeoff-evaluations$ 
```

Thinking it could have been a timing thing with Azure, I've tried waiting a few minutes between the clean command and trying to re-use the job store name, but it hasn't helped. Clean is still reporting success, and Toil is still telling me that I need to run clean.

diff --git a/src/toil/jobStores/azureJobStore.py b/src/toil/jobStores/azureJobStore.py
index b8d0c875..5a16194d 100644
--- a/src/toil/jobStores/azureJobStore.py
+++ b/src/toil/jobStores/azureJobStore.py
@@ -165,6 +165,7 @@ class AzureJobStore(AbstractJobStore):
         super(AzureJobStore, self).resume()
 
     def destroy(self):
+        self._bind()
         for name in 'jobItems', 'jobFileIDs', 'files', 'statsFiles', 'statsFileIDs':
             resource = getattr(self, name)
             if resource is not None:
['src/toil/jobStores/azureJobStore.py']