Remove test_shell_args.py
Remove test_shell_args.py

test_shell_args split up into specified files [1]. so this file
is not needed now.
This patch removes it.

[1]: Change-Id: I6b80b621311442df987e6ff031e8c77cf4bb7095

Change-Id: Iee3f4a4d83629c240ca77b8d278e1badd808a613
Closes-Bug: #1519167

openstack/python-magnumclient