Any valid HTTP response from Nailgun should be treated as if
Nailgun is operational, including 401.
Change-Id: I019a1c10583470064e14914158cc8582a2711ee4
Partial-Bug: #1585137
Co-Authored-By: Vitaly Kramskikh <vkramskikh@mirantis.com>
(cherry picked from commit 90ecd27260)