Renamed IsolationModule to Isolator.

Review: https://reviews.apache.org/r/9826

git-svn-id: https://svn.apache.org/repos/asf/incubator/mesos/trunk@1457164 13f79535-47bb-0310-9956-ffa450edef68
Changed master/slave::Flags to inherit from logging::Flags instead of
compose.

Review: https://reviews.apache.org/r/9931

git-svn-id: https://svn.apache.org/repos/asf/incubator/mesos/trunk@1457165 13f79535-47bb-0310-9956-ffa450edef68
Simplified constructing TestIsolator with only a single executor (the
common case) or no executors.

Review: https://reviews.apache.org/r/9932

git-svn-id: https://svn.apache.org/repos/asf/incubator/mesos/trunk@1457166 13f79535-47bb-0310-9956-ffa450edef68