Improve check which sees if Supervisor is running

Instead of just checking if the socket file exists, we should also check if the PID written to the PID file exists.
basic monitoring support for Apache Mesos
add get_ prefix and raise on missing url
basic monitoring support for Mesosphere Marathon
add instance tags
add instance tags
Add delete_misses/delete_hits to memcache

See https://github.com/memcached/memcached/blob/master/doc/protocol.txt,
there is delete_* stats we could use to report to datadog.
Merge pull request #928 from arthurnn/add_delete_memcache

Add delete_misses/delete_hits to memcache
Fix memcache test since new metrics have been added
Merge branch 'master' of https://github.com/DataDog/dd-agent
Merge pull request #919 from graemej/mesos_check

Basic monitoring support for Apache Mesos
Merge pull request #921 from graemej/marathon_check

Basic monitoring support for Mesosphere Marathon
Make docker integration compatible with latest versions of docker
Merge branch 'master' of https://github.com/DataDog/dd-agent
basic auth for couchdb integration
A few fixes to marathon and mesos checks
remove unneeded changes
Merge branch 'master' into couch_basic_auth
Merge pull request #931 from DataDog/couch_basic_auth

basic auth for couchdb integration
Merge pull request #901 from Tenzer/improve-supervisor-running-check

Improve check which sees if Supervisor is running