Turn 'check_who' into a decorator

This helper function seems to be more pretty/nice as
a decorator that is used uniformly instead of repeated
calling into it from needed functions.

Change-Id: If8aa2fb914cf80fdcecc37f044ab129d13f12be8

taskflow/jobs/backends/impl_zookeeper.py

@@ -55,11 +55,18 @@ TRASH_FOLDER = ".trash"
 JOB_PREFIX = 'job'
 
 
-def _check_who(who):
-    if not isinstance(who, six.string_types):
-        raise TypeError("Job applicant must be a string type")
-    if len(who) == 0:
-        raise ValueError("Job applicant must be non-empty")
+def check_who(meth):
+    """Decorator that checks the expected owner type & value restrictions."""
+
+    @six.wraps(meth)
+    def wrapper(self, job, who, *args, **kwargs):
+        if not isinstance(who, six.string_types):
+            raise TypeError("Job applicant must be a string type")
+        if len(who) == 0:
+            raise ValueError("Job applicant must be non-empty")
+        return meth(self, job, who, *args, **kwargs)
+
+    return wrapper
 
 
 class ZookeeperJob(base.Job):
@@ -535,6 +542,7 @@ class ZookeeperJobBoard(base.NotifyingJobBoard):
             self._emit(base.POSTED, details={'job': job})
             return job
 
+    @check_who
     def claim(self, job, who):
         def _unclaimable_try_find_owner(cause):
             try:
@@ -547,7 +555,6 @@ class ZookeeperJobBoard(base.NotifyingJobBoard):
                 msg = "Job %s already claimed" % (job.uuid)
             return excp.UnclaimableJob(msg, cause)
 
-        _check_who(who)
         with self._wrap(job.uuid, job.path, "Claiming failure: %s"):
             # NOTE(harlowja): post as json which will allow for future changes
             # more easily than a raw string/text.
@@ -626,8 +633,8 @@ class ZookeeperJobBoard(base.NotifyingJobBoard):
         return (misc.decode_json(lock_data), lock_stat,
                 misc.decode_json(job_data), job_stat)
 
+    @check_who
     def consume(self, job, who):
-        _check_who(who)
         with self._wrap(job.uuid, job.path, "Consumption failure: %s"):
             try:
                 owner_data = self._get_owner_and_data(job)
@@ -646,8 +653,8 @@ class ZookeeperJobBoard(base.NotifyingJobBoard):
             kazoo_utils.checked_commit(txn)
             self._remove_job(job.path)
 
+    @check_who
     def abandon(self, job, who):
-        _check_who(who)
         with self._wrap(job.uuid, job.path, "Abandonment failure: %s"):
             try:
                 owner_data = self._get_owner_and_data(job)
@@ -664,8 +671,8 @@ class ZookeeperJobBoard(base.NotifyingJobBoard):
             txn.delete(job.lock_path, version=lock_stat.version)
             kazoo_utils.checked_commit(txn)
 
+    @check_who
     def trash(self, job, who):
-        _check_who(who)
         with self._wrap(job.uuid, job.path, "Trash failure: %s"):
             try:
                 owner_data = self._get_owner_and_data(job)