Add 'max_num_executors' flag for use with network isolation

Review: https://reviews.apache.org/r/24128
Fixed two flaky tests in GarbageCollectorIntegrationTest.

Review: https://reviews.apache.org/r/24350
Added a trailing space to _CheckFatal's output.

- So there is a space between the error message and the additional message appended after the check. e.g. CHECK_SOME(None()) << "Some additional message";
- GLOG CHECK adds this space too: https://code.google.com/p/google-glog/source/browse/trunk/src/glog/logging.h.in#561

Review: https://reviews.apache.org/r/24355
Fixed docker validation and only run docker tests on linux with root.

Review: https://reviews.apache.org/r/24361
Made ephemeral ports a resource and killed private resources.

Review: https://reviews.apache.org/r/24269
Do not send ephemeral_ports resource to frameworks.

Review: https://reviews.apache.org/r/24286
Create static mesos library.

Review: https://reviews.apache.org/r/24252
Re-enabled HealthCheckTest.ConsecutiveFailures test.

The test originally was flaky because the time to process the number
of consecutive checks configured exceeds the task itself, so the task
finished but the number of expected task health check didn't match.

Review: https://reviews.apache.org/r/23772
Add ContainerInfo and Volumes proto defs