Handle pid in run_single_worker.rb properly

In classes that inherit from MiqQueueWorkerBase, they will fetch images
using `MiqQueue.get`.  Part of what is done in that is calling
`MiqWorker.my_worker`.  This basically makes a call to find a worker
with the `pid` value that matches the same pid used by the current
process.

Unfortunately, this is normally set by the `MiqServer` prior to forking
the worker, so this isn't set by `run_single_worker.rb`.

To address this, either add to the `create_options` an attribute for
`:pid` that will create a new worker with the existing pid of the
current process, or if a `:guid` is passed in, update the attributes of
the existing worker to set the pid.  This is already done by the
`MiqServer`, so this is just making the `run_single_worker.rb` handle
setting the pid as well.

lib/workers/bin/run_single_worker.rb

@@ -57,7 +57,7 @@
 worker_class = worker_class.constantize
 worker_class.before_fork
 unless options[:dry_run]
-  create_options = {}
+  create_options = {:pid => Process.pid}
   runner_options = {}
 
   if ENV["QUEUE"]
@@ -66,7 +66,9 @@
   end
 
   worker = if options[:guid]
-             worker_class.find_by!(:guid => options[:guid])
+             worker_class.find_by!(:guid => options[:guid]).tap do |wrkr|
+               wrkr.update_attributes(:pid => Process.pid)
+             end
            else
              worker_class.create_worker_record(create_options)
            end