Prepare for enabling H302 rule(services/compute/v3/json)

Currently H302 rule is ignored by tox. However, this rule should
be enabled. This patch partially fixes this problem to prepare for
H302 rule.

Change-Id: I4f573cb306f86cf8476f8fa8950a47c21e443db8
Prepare for enabling H302 rule(api/image)

Currently H302 rule is ignored by tox. However, this rule should
be enabled. This patch partially fixes this problem to prepare for
H302 rule.

Change-Id: Ieb47937ae222e3ccf8d8c630f344a64db8d256ba
Merge "Prepare for enabling H302 rule(services/compute/v3/json)"
Merge "Prepare for enabling H302 rule(api/image)"
Merge branch 'master' of https://github.com/openstack/tempest