Add helper in tests/mesos.hpp to create task with resources

Review: https://reviews.apache.org/r/22048
Ignore slave cgroup during isolator recovery.

Do not consider the slave cgroup (from --slave_subsystems) as an orphan
during recover().
Added process ID prefixes for ZooKeeper related libprocess Processes which are helpful for debugging.

Review: https://reviews.apache.org/r/22161