warn the user when docker is not locally installed

also update the documentation
also support ipv6

and grab first vm ip for connection
stash conflict.
use ssh ControlMaster to differenciate channels

this fixes --vm that was broken
use a dynamic port for remote vms

This should go towards allowing concurrent docker usage with less bugs.
fix unixpipe failure with unix socket connection

close child fd from parent to avoid blocking client
catch and display socket errors nicely
Use DOCKER_HOST and be verbose about that

using DOCKER_HOST after tunnel setup is an option for the user.
refactor brainfuck
add a few style fixes
Merge pull request #11 from kalou/docker-fixes

Various fixes for gandi vm docker command
Use echo method instead of print
Use list comprehension when possible
use "Exception as err".

we are in python 2.6 minimum.
PEP8
try python 3
Merge pull request #12 from grigouze/exception_as

unixpipe: use modern Exception "as" + PEP8
add a new line
Merge pull request #13 from grigouze/newline_for_development_section

Fix README file
Don't save sshkey filepath in configuration if invalid during setup.
Custom option parameters should check for valid configuration.

This caused a problem when using vm creation command without configuration,
displaying an error about invalid datacenter value.