Add error checking to get_terminal_size.

Adds returncode error checking to get_terminal_size so that
it doesn't spew errors to console when running glance commands
in a shell without a TTY.

Fixes LP Bug #956202.

Change-Id: I42e155d168da1f4f25c0dea9ad9768686bd654ce

glance/common/utils.py

@@ -326,7 +326,9 @@ def _get_terminal_size_posix():
                 p = subprocess.Popen(['stty', 'size'],
                                     shell=False,
                                     stdout=subprocess.PIPE)
-                return tuple(int(x) for x in p.communicate()[0].split())
+                result = p.communicate()
+                if p.returncode == 0:
+                    return tuple(int(x) for x in result[0].split())
             except:
                 pass