Ignore command line arguments that are not flags.

Review: https://reviews.apache.org/r/14812
Moved src/mesos to src/cli.

Review: https://reviews.apache.org/r/14813
Added 'mesos::internal::detect' for CLI tools.

Review: https://reviews.apache.org/r/14814
Added an 'HDFS' abstraction.

Review: https://reviews.apache.org/r/14815
Made 'mesos' be a "subcommand dispatcher" and added the 'resolve',
'execute' and 'ps' subcommands.

Review: https://reviews.apache.org/r/14816