Revamp Docker check, more metrics, less bugs, support of CoreOS
Wincpu| Switch to psutil to collect user, idle and system cpu
WinCPU| Don't rely on psutil form call to call
Clarify Docker check exception messages
Find croup file at first check instead of init

Also some minor fixes
Reorganize imports
Allow checks to have a minimum collection interval

To make sure they don’t run to often.

This is NOT a fully customizable check interval for a check.
It just allows to specify a minimum interval of time between 2
iterations of a check/instance.

See #797
Merge pull request #1043 from DataDog/docker-revamp

Revamp Docker check, more metrics, less bugs, support of CoreOS
Clean the dist directory before each build
Deprecate pup
Update CHANGELOG with Docker changes
WinCPU| Compute average accross the time between collection
WinCPU| Don't forget the factor 100
Support HA mode for hdfs check

Fix #1018
Remove star import
update change log
Exclude dlls
Add host metadata when sending agent checks
Merge pull request #1047 from DataDog/rudy/win-getaddr

Resolve connection issues on windows 2008 sp2
init config should never be None