Added explicit DockerInfo within ContainerInfo.

Added new DockerInfo to explicitly capture Docker options, and allow
command URIs to be fetched and mapped into sandbox, which gets
bind-mounted into the container.

Review: https://reviews.apache.org/r/24475
Used new CommandInfo with Docker::run.

Review: https://reviews.apache.org/r/24673
Fix for configure --disable-python
MESOS-1693: enable build against non-x86 arch

Enable building against non-x86 arch, namely arm builders on Fedora.

Review: https://reviews.apache.org/r/24563
Fixed a few compiler warnings in stout.
Redirect Docker logs.