Change default log level from INFO to WARNING

[omry]

Closes #1262.

The default log level for Python apps is WARNING (per Python docs). Hydra no longer sets the log level of the root logger to ensure it does not change this behavior.
This is a breaking change, people relying on the previous behavior can configure the log level on their own side by adding something like this to their config:

hydra:
  job_logging:
    root:
      level: INFO

[omry]

@JackUrb, thinking about his some more. I think am will not proceed with this change.

Hydra is configuring the logging so you don't have to. The default log level in Python (WARNING) is not very useful in my opinion.
If you would like to control the log level you can do it by overriding the root log log level in hydra/job_logging. You can also do it for individual loggers.

loggers:
  sh:
    level: WARNING

[omry]

I am abandoning this.
Hydra is configuring the logging to to something that is useful for the majority of the applications by default.
I think INFO level for the root logger is a useful default.

Applications that does like the default behavior has two options:

1. Customize the logging configuration to match their needs.
2. Completely disable the logging configuration (see Implemented disabling logging configuration & added config file #1130 to see how, this will be easier in 1.1)