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Also, fix typos and default values for service configurations

Refs: #3874

Let cross-service initializations to use explicit service endpoint urls if
there is no single authentication url.
- In Image commands, there are calls that use astakos and pithos clients
- In pithos there are calls that use astakos client

Refs: #3874

In current configuration, kamaki checks for auth_url. If that fails,
it raises an error. If it is not set, it prints a warning and attempts
to read the <service>.url option from the configuration file.

Service urls: astakos.url, pithos.url, cyclades.url, plankton.url

Refs: #3913

Config file can (optionaly) contain:

[remotes]
 example = https://www.example.org/astakos/identity/v2.0/
 old_version = https://www.example.org/astakos/identity/v1.0/
 ...

Now, user can explicitely request for a remote cloud authentication URI:

kamaki --cloud=<remote>

Refs: #3874

Use kamaki.clients.astakos.AstakosClient as a cached astakos client to get
user information and, most importantly, endpoints. Allow users to authenticate
multiple tokens on the same session. In every session there must be at most
one authentication per user/token.

Major change: top kamaki.cli.commands class now contains a base_auth field
with the cached authenticating client. All urls are drained from this field.

Refs: #3874

Minimum config file:
[global]
token = <user token>

Changes:

- Only one field "cli" for user command specs, to map command groups to CLIs:

[cli]
 user = astakos
 file = pithos
 server = cyclades
...

- Specify client services/apis and versions.
 General format:
 [client]
  type = <service>
  version = <api version>

 Example:
 [cyclades]
  type = compute
  version = v2.0

Conflicts:
	Changelog
	version

Refs: #3874

Kamaki.clients.astakos.AstakosClient is now a high-level client lib that
offers access to token-authenticated astakos-aquired cached information.
Users who need an astakos client should use the snf-astakosclient instead.

Usage:

 astakos_cache = AstakosClient(<astakos/base/url/with/identity/api>)
 astakos_cache.authenticate(<token>)
 user_info = astakos_cache.user_info()
 compute_endpoints = astakos_cache.get_service_endpoints('compute', 'v2')

Major changes:

Modify ReST call from /im/authenticate to /tokens

New methods as AstakosClient instance cache accessors:
 get_services
 get_service_details
 get_service_endpoints

Method renaiming for existing AstakosClient instance cache accessors:
 info --> user_info
 user --> list_users

Methods exposed:

get_user_info as authenticate
get_uuid[s] as uuid
get_username[s] as username
get_quotas as quotas
services_get_uuid[s]/username[s]/quotas as service uuid/username/quotas

Refs: #3633

- Meta-->metadata in some cases, according to the expected cyclades API
- remove values level from requests and responses @ cyclades lib

Refs: #3633

- validate image metadata format
- read metadata from file
- merge file-loaded metadata with runtimes
- store metadata file on pithos, check existance, overwrite with -f
- raise helpful error messages when there fail

Refs: #3797

- Ensure uniform image meta output
- Easy to apply the correct meta format

Refs: #3797

Conflicts:
	Changelog
	kamaki/cli/commands/image.py

Also, take care of pep8 issues

Refs: #3732

Refs: #3732