Glance client does not correctly forward global request IDs

This is about the Global Request ID functionality of OpenStack [1].

When the Glance client is used to instantiate a client object for
accessing the Glance API, a global_request_id parameter may be
passed to it. However, due to a coding error in the SessionClient
class, the parameter never reaches the Glance API in form of the
"X-Openstack-Request-Id" header and is instead lost.

# How to reproduce

This can be reproduced simply by creating a server in Nova from an
image in Glance, which will attempt to create the Glance client
instance using the global_request_id [5]. Passing the
"X-Openstack-Request-Id" header during the initial API call for the
server creation, makes it visible in Nova (using a suitable
"logging_context_format_string" setting) but it's not visible in
Glance. Using a Python debugger shows Glance generating a new local ID
instead.

Example for a "logging_context_format_string" showing both IDs:

logging_context_format_string = %(levelname)s %(name)s [%(request_id)s | %(global_request_id)s %(user_identity)s] %(instance)s%(message)s

Note: due to another bug in Glance API, currently the global request
id will never actually show up as %(global_request_id)s in Glance API
but will instead be shown as the %(request_id)s if available, i.e. when
this client bug gets fixed, a global id will show up in the logs as if
it was a local one until the API bug is fixed too. So expect different
behavior when applying this logging setting to both Nova and Glance!

# Technical details

When the SessionClient class is used, the global_request_id is removed
from kwargs in the constructor using pop() [2]. Directly after this,
the parent constructor is called using super(), which in this case is
Adapter from the keystoneauth1 library. Therein the global_request_id
is set again [3] but since it has been removed from the kwargs, it
defaults to None as specified in the Adapter's __init__() header. Thus,
the global_request_id passed to the SessionClient constructor never
actually makes it to the Glance API. This is in contrast to the
HTTPClient class, where get() is used instead of pop() [4].

# Proposed solution

Replace pop() by get() in the code of SessionClient referenced above.

# Link references

[1] https://specs.openstack.org/openstack/oslo-specs/specs/pike/global-req-id.html
[2] https://github.com/openstack/python-glanceclient/blob/de178ac4382716cc93022be06b93697936e816fc/glanceclient/common/http.py#L355
[3] https://github.com/openstack/keystoneauth/blob/dab8e1057ae8bb9a0e778fb8d3141ad4fb36a339/keystoneauth1/adapter.py#L166
[4] https://github.com/openstack/python-glanceclient/blob/de178ac4382716cc93022be06b93697936e816fc/glanceclient/common/http.py#L162
[5] https://github.com/openstack/nova/blob/1cae0cd7229207478b70275509aecd778ca69225/nova/image/glance.py#L78