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
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
Allow optional custom tags in SQL Server check.
Made postgres database name configurable.
Fixes issue #523.
bump version to 3.9.3
Merge pull request #646 from morskoyzmey/patch-1

Add CPU percent and threads number metrics
Display a warning if the cpu_check_interval is not a number
Merge pull request #643 from stefan-mees/master

add riak 1.3.2 metrics to monitor new "Overload Protection / Work Sheddi...
Fetch the Mongo database name from the URI.
Merge pull request #657 from DataDog/mongo_db_config

Fetch the Mongo database name from the URI.
Add unit to the forwarder info page for the queue size (fix #650)
Merge pull request #590 from micktwomey/mysql-config-from-defaults-file

Allow MySQL check configuration via a mysql config file
Get rid of unnecessary line when parsing for old config in the mysql check
Get rid of unnecessari functionality.

You can use
```
python agent.py check network
```
 to get the same result
Rename method to reflect reality