When sending NoMasterDetectedMessage, we need to clear the master
sequence number in order to ensure we still send
NewMasterDetectedMessage if the master is the same. Otherwise, we can
get stuck in a master-less state.

Review: https://reviews.apache.org/r/10161

git-svn-id: https://svn.apache.org/repos/asf/incubator/mesos/trunk@1477440 13f79535-47bb-0310-9956-ffa450edef68
Removed the unused SlavesManager and SlaveRegistrar code, to be added
later with MESOS-295.

Review: https://reviews.apache.org/r/10171

git-svn-id: https://svn.apache.org/repos/asf/incubator/mesos/trunk@1477441 13f79535-47bb-0310-9956-ffa450edef68
Send NoMasterDetectedMessage on session timeout to non-contending
detectors. Added a disconnected slave map to the master to track
disconnected slaves, in order to disallow slave re-registration after
a network partition.

Review: https://reviews.apache.org/r/10172

git-svn-id: https://svn.apache.org/repos/asf/incubator/mesos/trunk@1477442 13f79535-47bb-0310-9956-ffa450edef68
Removed the hostname:port slave map from the Master.

Review: https://reviews.apache.org/r/10534

git-svn-id: https://svn.apache.org/repos/asf/incubator/mesos/trunk@1477443 13f79535-47bb-0310-9956-ffa450edef68