Fix SimpleReadOnlyNovaManageTest.test_flavor_list CLI test

'nova-manage flavor list' should equal 'nova-manage instance_type list'

Adds an option, merge_stderr, that when enabled redirects stderr to
stdout.

Fix bug 1159914

Change-Id: Icfb93f3fd1f1d6f14a73b4873a6dad36122d3a98
Merge "Fix SimpleReadOnlyNovaManageTest.test_flavor_list CLI test"