Use Docker official IANA ports

Docker now has official IANA ports and these should be used instead
http://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml?search=docker
Fix issue with image directory creation task race
wip - fix deployment on GCE

update docker port to official IANA
Merge pull request #25 from brooklyncentral/fix/issue20

wip for issue #20
Fix use of provisioning flags to choose Ubuntu OS
Merge pull request #21 from cpuguy83/patch-1

Use Docker official IANA ports
update readme
update README
Merge pull request #26 from brooklyncentral/updateREADME

updated to ensure it is self-contained for first time users
Automatically map PortAttributeSensorAndConfigKey attributes
Fail DockerHost setup if customisation exit code is not zero

Without the check the next step will fail instead, which is a bit
misleading when you're debugging.
Use MachineEntity for DockerHost parent
Merge pull request #27 from sjcorbett/detect-port-mapping

Detect port mapping
Merge pull request #24 from brooklyncentral/fix/provisioning-flags

Fix use of provisioning flags to choose Ubuntu OS
Fix logger name
Update README.md

Added an explicit Getting Involved section
Add mapped sensor details for Nginx to YAML blueprint
Save template for DockerHost location
Tidy up whitespace and fix setting entity context
Fix use of sudo in Docker command execution