add agent.up service check
check for root user (issue #1605)
use boolean instead of string
use alias to no-op sudo for root user
use a variable for sudo command since (alias sudo='') didnot work
Bugfix: handle case where pg_last_xact_replay_timestamp is null

It could sometimes be null
see http://www.postgresql.org/message-id/201012081137.52066.gabi.julien@broadsign.com
Merge pull request #961 from DataDog/tristan/elasticcheck

Bugfix: handle case where pg_last_xact_replay_timestamp is null
update postgre source type name to postgresql
Merge pull request #954 from DataDog/default-service-checks

add agent.up service check
upgrade to cassandra 2.0.8 in travis test

they removed 2.0.7 from the repo
Merge branch 'isaac/check_for_root_user'
Merge branch 'master' into omnibus_bundling