Allow MySQL check configuration via a mysql config file

For more complex configuration (e.g. specifying SSL certificates) it's
useful to use a mysql.cnf instead of specifying flags by hand.
add riak 1.3.2 metrics to monitor new "Overload Protection / Work Shedding" feature
Made http_check aware of tags passed in the yaml, instead of using the URL as a sole tag.
Add CPU percent and threads number metrics
More precise cpu persentage
x2 more precise cpu persentage
Configurable CPU check interval
Add cpu_check_interval for CPU percent usage
Made http_check aware of tags passed in the yaml, instead of using the URL as a sole tag.
Merge branch 'master' of github.com:ordenull/dd-agent
Fixed mistakes in the http check.
Raise an exception is varnish check is not properly configured
Merge pull request #647 from ordenull/master

Made HTTP check tag aware
Make a pause when restarting the agent to give enough time for the agent to clean itself
Merge branch 'master' of github.com:DataDog/dd-agent
Reduce sleeping time when restart
Update datadog-agent.init
Sleep to give enough time for the daemon to stop cleanly
bump version to 3.9.3
Merge pull request #646 from morskoyzmey/patch-1

Add CPU percent and threads number metrics