Add support for location parameters in v2 commands

Currently glanceclient's v2 commands don't support modification
operations on an image's location attribute - the argparse specification
for the location attribute of the image-update command causes the image
id argument to be included in list of locations and so the command
parsing fails (because it causes the image id to appear to be missing).

Furthermore even if the 'locations' argument were to be accepted by
argparse (e.g. by changing the argument specs and using --id to specify
the image id) the command would still fail because the arguments are
passed directly to the schema which expects the value of the 'locations'
argument to be a valid dictionary (there is nobody to convert the
argument string to a python dictionary that the schema expects).

This commit adds the following location related commands to
glanceclient:
    --location-add: Add a new location to the list of image locations.
    --location-delete: Remove an existing location from the list of
        image locations.
    --location-update: Update the metadata of existing location.

The glanceclient.v2.images.Controller class has been agumented with
three new methods to support the commands listed above:
    - add_location
    - delete_locations
    - update_location

The server has not been modified, i.e. all location related API requests
are passed to the server via HTTP PATCH requests and handled by the
server's image update function.

The v2 'image' and 'shell' related tests have also been supplemented.

Note that in order to use these options the server must be first
configured to expose location related info to the clients (i.e.
'show_multiple_locations' must be set to 'True").

I also added a mailmap entry for myself.

DocImpact
Closes-bug: #1271452
Co-Author: David Koo (koofoss) <david.koo@huawei.com>

Change-Id: Id1f320af05d9344645836359758e4aa227aafc69
Merge "Add support for location parameters in v2 commands"