Move providers information into config

[spinillos]

To archive that we needed to change the way to create the providers. The constructor doesn't check the missing configuration and it was moved into a validate function. This function is called internally when we do want to do queries to the resources.

Now configuration has two new options:

grr config providers handlers
grr config providers status

Maybe validate needs a better name since is exposed to make status to work.

• handlers is the old grr providers command but showing all providers information instead of the active ones (the ones with the full configuration set).
• status shows the information that it showed all the time when you execute any command showing if the provider is active or not.

[malcolmholmes]

I wonder it "kinds" is a better name than "handlers", with handlers being an internal name. What people will care about is the kinds that Grizzly supports (and the providers they must configure).

[spinillos]

Its added because start_period works from 3.4