Fixes volume attach issue on Hyper-V

Fixes Bug: #1074717

During volume attach on Windows a process is spawned. The process
currently fails with the following exception, due to eventlet monkey
patching of the os module.

NotImplementedError: set_nonblocking() on a file object with no
setblocking() method (Windows pipes don't support non-blocking I/O)

The fix consists in avoiding monkey patching the os module in
nova-compute on Hyper-V

Change-Id: Ib513bc218da83b751439bad114baac24b08e3d02

bin/nova-compute

@@ -20,7 +20,14 @@
 """Starter script for Nova Compute."""
 
 import eventlet
-eventlet.monkey_patch()
+import os
+
+if os.name == 'nt':
+    # eventlet monkey patching causes subprocess.Popen to fail on Windows
+    # when using pipes due to missing non blocking I/O support
+    eventlet.monkey_patch(os=False)
+else:
+    eventlet.monkey_patch()
 
 import os
 import sys