Modify code to prepare HTTPS migration

[louisjdmartin]

Following the last meeting here some change that can already be done in DIRAC for HTTPS migration.

It also include a whoami method for services.

BEGINRELEASENOTES

*CS
CHANGE: Separation between threads an logic in Refresher
CHANGE: Separation between threads an logic in ServiceInterface
NEW: Client for Configuration/Server

*Core
NEW: adding new way to detect url in Core.Base.Client (using a kwargs)
NEW: a simple whoami for services

ENDRELEASENOTES

[coveralls]

Coverage increased (+0.009%) to 20.685% when pulling 6f8b416 on louisjdmartin:pr_to_dirac into d7aa596 on DIRACGrid:integration.

[fstagni]

Using here

self.setServer('Configuration/Server')

wouldn't work?

[louisjdmartin]

Sometime component need to provide an explicit url (for example, the master configuration server choose a slave server to ping it). This line may override the url given from **kwargs with a random url from CS.
But I can add this:

  def __init__(self, **kwargs):
    if 'url' not in kwargs:
      kwargs['url'] = 'Configuration/Server'
    super(ConfigurationServerClient, self).__init__(**kwargs)

So by default it use an URL from the CS, but it still possible to give another URL on the keywords arguments.

[fstagni]

The release notes should mention which DIRAC system is involved.

[atsareg]

This PR should be dropped as replcaed by #3815, shouldn't it ?

[chaen]

Yes :)