Earlier glance help <subcommand> was listing required arguments as
optional arguments in help text. Added new argument group to list
required argument properly.

$ glance help stores-delete

Example before this change:
usage: glance stores-delete --store <STORE_ID> <IMAGE_ID>

Delete image from specific store.

Positional arguments:
  <IMAGE_ID>          ID of image to update.

Optional arguments:
  --store <STORE_ID>  Store to delete image from.

After this change:
usage: glance stores-delete --store <STORE_ID> <IMAGE_ID>

Delete image from specific store.

Positional arguments:
  <IMAGE_ID>          ID of image to update.

Required arguments:
  --store <STORE_ID>  Store to delete image from.

Change-Id: I51ea4c43fa62164ed43e78d1ae0fb0cb2521fc83
Closes-Bug: #1933390

Using the glanceclient without a subcommand while
passing an optional argument triggers the raw Python
error `ERROR: 'Namespace' object has no attribute
'func'`. This bug can be reproduced by issuing the
command `glance --os-image-api-version 2`.
Added a default value to `func` as placeholder
so that a help message is shown instead of the Python error.

Closes-Bug: #1903727
Change-Id: Ie4288262e408192310cbbc240bd1779b265a64fd

Change-Id: I3dbfcfa0f5f590a41ed549afd44537d8ed41433a

The __future__ module [1] was used in this context to ensure compatibility
between python 2 and python 3.

We previously dropped the support of python 2.7 [2] and now we only support
python 3 so we don't need to continue to use this module and the imports
listed below.

Imports commonly used and their related PEPs:
- `division` is related to PEP 238 [3]
- `print_function` is related to PEP 3105 [4]
- `unicode_literals` is related to PEP 3112 [5]
- `with_statement` is related to PEP 343 [6]
- `absolute_import` is related to PEP 328 [7]

[1] https://docs.python.org/3/library/__future__.html
[2] https://governance.openstack.org/tc/goals/selected/ussuri/drop-py27.html
[3] https://www.python.org/dev/peps/pep-0238
[4] https://www.python.org/dev/peps/pep-3105
[5] https://www.python.org/dev/peps/pep-3112
[6] https://www.python.org/dev/peps/pep-0343
[7] https://www.python.org/dev/peps/pep-0328

Change-Id: I732a57361319687ca0a64693f0e60bc0d8f5b3d2

Old deprecated ssl options block the new keystoneauth parser get the
correct value, should be removed.

Change-Id: Ie080f9a8fa7f4407b1fcbb7fb7c763152c5ec295
Closes-Bug: 1697163

--no-ssl-compression is deprecated and no longer used. So, it is
removed from the help message.

Change-Id: I2b886671a568ed191ee380cf16335ccd9ae85062
Closes-Bug: #1583919

--profile argument can be loaded from OS_PROFILE environment variables
to avoid repeating --profile in client commands.

Correct/update help text.

Co-Authored-By: Hieu LE <hieulq@vn.fujitsu.com>
Change-Id: I67c1e4b859b972e380eb658c98ceae4fbef5c254