Any error in k8s is returned as 500 from magnum api

[Ryan Rossiter]

To reproduce:

Bring up k8s bay

Run magnum pod-create --manifest ./redis-master.yaml --bay k8sbay
  - Change apiVersion to something that is not the api version being used

Expected Result:
Magnum API returns error message from Kubernetes as to why it failed

Actual Result:
Magnum API returns 'ERROR: 'NoneType' object has no attribute 'host' (HTTP 500)'

(Kubernetes returns: {u'status': u'Failure', u'kind': u'Status', u'code': 400, u'apiVersion': u'v1beta3', u'reason': u'BadRequest', u'message': u'Pod in version v1 cannot be handled as a Pod: no kind "Pod" is registered for version "v1"', u'metadata': {}})

In https://github.com/openstack/magnum/blob/master/magnum/conductor/handlers/k8s_conductor.py it looks like every k8s api call is wrapped in a try with an except on HTTPError. When k8s encounters any problem, it just puts the error in the response without raising an exception, so conductor keeps rolling assuming the call went OK. This results in the API returning 500 errors with very non-specific error messages.

These try blocks around k8s calls are for every operation in the k8s conductor handler, so any failure on those operations in k8s will result in a 500.