Make Windows agent use multiple processes instead of threads.

Fixes #684
Fix certificate path when running win agent locally.

Assumes you're running from the root directory of the dd-agent repo.
Enable freeze support in multiprocessing.
Fix getting WMI connections.
Downgrade missing IIS metric to a debug message.

Some old versions of Windows (e.g. 2k3) are always missing certain
metrics so this avoids spitting out the same error over and over again.
Restart processes that die unexpectedly.
Auto-restart the collector after 1 day.

* Workaround for the memory leak affecting Win 2k3.
* Will *not* submit a start even on restart.
Prevent spawning lots of Collector processing on auto-restart.
Always treat restart interval as an int.
Log the auto-restart interval on start.
Make procs a dictionary so we don't have to worry about indices.
Merge pull request #702 from DataDog/win32_multiprocessing

Split Windows agent into multiple processes.