Don't attempt to read stdin if it is empty.

* Check for available data size in v1/shell.py/_set_data_field, don't
   read if 0.
 * Add test_shell.py including tests for 3x stdin scenarios:
	* closed
 	* open and empty
	* open with data

Change-Id: I6ff65b0e226be509de9cd3f021560081529283b0
Fixes: bug #1173044

glanceclient/v1/shell.py

@@ -121,12 +121,12 @@ def _set_data_field(fields, args):
             # (3) no image data provided:
             #     glance ...
             try:
-                os.fstat(0)
+                stat_result = os.fstat(0)
             except OSError:
                 # (1) stdin is not valid (closed...)
                 fields['data'] = None
                 return
-            if not sys.stdin.isatty():
+            if not sys.stdin.isatty() and stat_result.st_size != 0:
                 # (2) image data is provided through standard input
                 if msvcrt:
                     msvcrt.setmode(sys.stdin.fileno(), os.O_BINARY)