Adds Localsensor to PoweredByMesos documentation.
Pass executor directory to Isolator::prepare().

Review: https://reviews.apache.org/r/24177
Serialize isolator prepare and cleanup (reversed).

Review: https://reviews.apache.org/r/25861
Remove /proc and /sys remounts from port_mapping isolator.

Review: https://reviews.apache.org/r/26274
Introduce a shared filesytem isolator.

Isolator supports creating private copies of system directories, e.g.,
/tmp, for each container while sharing the host's filesystem.

Review: https://reviews.apache.org/r/25549
Add Artirix to PoweredByMesos list.
Added --isolation flag for tests.

This is useful to test custom isolation modules with the test suite.
The user can specify the available modules with --modules and then he
can specify the isolator module with the --isolation flag.
With these flags, the test suite will run all tests with the specified
isolator modules.

Review: https://reviews.apache.org/r/26797
Added support for module-specific command-line parameters.

The Modules protobuf is enhanced to support key-value parameters based
on mesos::Parameter and mesos::Parameters.

Bumped Module API version since we modified the signature of the
create() method.

Review: https://reviews.apache.org/r/27051