Add async fork

Change-Id: Ib81697fbef0ed1fc803a36c7489b998cba63cfba

.gitignore

@@ -2,4 +2,5 @@
 *.pyc
 dist/
 *.egg-info/
+*.egg/
 build/

rackclient/v1/syscall/default/syscall.py

@@ -1,10 +1,20 @@
+import threading
 from rackclient import process_context
 from rackclient.v1.syscall.default import pipe as rackpipe, file as rackfile
 
 PCTXT = process_context.PCTXT
 
 
-def fork(pid=PCTXT.pid, **kwargs):
+def fork(pid=PCTXT.pid, is_async=False, **kwargs):
+    if is_async:
+        th = threading.Thread(target=_fork, args=[pid], kwargs=kwargs)
+        th.start()
+        return th
+    else:
+        return _fork(pid, **kwargs)
+
+
+def _fork(pid, **kwargs):
     child = PCTXT.client.processes.create(gid=PCTXT.gid, ppid=pid, **kwargs)
     rackpipe.Pipe.share(pid, child.pid)
     return child