--os-image-api-version 2 behaviour inconsistent

[Stuart McLaren]

If only v1 is available and the schema has been cached, then this command will produce:

$ glance --os-tenant-name=blah --os-username=blah --os-auth-url=blah --os-region region-a.geo-1 --os-image-api-version 2 image-show d6bc96f0-70da-432b-a27c-dcf99d61ef0d
HTTPMultipleChoices (HTTP 300) Requested version of OpenStack Images API is not available.

If the schema is not cached, the behaviour is:

$ glance --os-tenant-name=blah --os-username=blah --os-auth-url=blah --os-region region-a.geo-1 --os-image-api-version 2 image-show d6bc96f0-70da-432b-a27c-dcf99d61ef0d
WARNING: The client is falling back to v1 because the accessing to v2 failed. This behavior will be removed in future versions
+------------------+--------------------------------------+
| Property | Value |
+------------------+--------------------------------------+
| checksum | a16a81de3d944ebee63810f36b826a63 |
| container_format | bare |
| created_at | 2014-07-31T12:48:53 |
| deleted | False |
| disk_format | raw |
| id | d6bc96f0-70da-432b-a27c-dcf99d61ef0d |
| is_public | False |
| min_disk | 0 |
| min_ram | 0 |
| name | x |
| owner | 61624292678963 |
| protected | False |
| size | 1048576000 |
| status | active |
| updated_at | 2014-07-31T12:49:47 |
+------------------+--------------------------------------+

If the user explicitly selects the API version on the command line (--os-image-api-version 2) the appropriate behaviour is to return "HTTPMultipleChoices (HTTP 300) Requested version of OpenStack Images API is not available." in all cases where it is not available.

[Stuart McLaren (stuart-mclaren)]

Overall, I think the behaviour should be:

glance --os-image-api-version 1 ... -> fail if version 1 is not available
glance --os-image-api-version 2 ... -> fail if version 2 is not available
glance ... -> The user has expressed no preference. Query the endpoint to see if v2 is available -- if so, use it. If not, is v1 available? If so, use it.

It's important that if a user explicitly selects an api version that we fail if that version is not available.

For example an operator may have monitoring scripts such as:

script 1:
# ensure v1 is responsive
glance --os-image-api-version 1 ...

script 2:
#ensure v2 is responsive
glance --os-image-api-version 2 ...

if 'script 2' works by falling back to v1 in this case there's no way for the operator to use the client cli to verify v2 is alive.

[Flavio Percoco (flaper87)]

Stuart, I believe these 2 patches[0][1] fix this issue as well. Could you help me verifying it?

If so, I'll add the bug number to the first patch. This is also tested in that one.

[0] https://review.openstack.org/#/c/219469/
[1] https://review.openstack.org/#/c/219686/