Check the MongoDB connection and send the service check
Add MySQL service check
Add service check for SQLServer
Revert "Check the MongoDB connection and send the service check"

This reverts commit 90eaebfc713b050cdde0545093e5e7f3abdbb30b.
Merge branch 'master' into db-service-checks

Conflicts:
	checks.d/mysql.py
Add service check for MongoDB
Clean mongo check code
Add test for Mongo sc
Add test for Mysql sc
Add test for SQLServer sc
Fix Travis build for test_mongo.py
Fix typo that made the Travis build fail
Merge branch 'master' into db-service-checks
Merge with master and fix service checks
Fix mongo service checks
Use check constant instead of hardcoded value
Merge with master
Merge pull request #1053 from DataDog/db-service-checks

DB default service checks