Clean up handling of argv in tests

[glasserc]

kinto-wizard/tests/test_functional.py

Lines 23 to 26 in 762c573

	cmd = 'kinto-wizard {} --server={} --auth={} --dry-run'
	load_cmd = cmd.format("load {}".format(self.file),
	self.server, self.auth)
	sys.argv = load_cmd.split(" ")

This sort of stuff seems a little bit like bad practice..