Added a VerifyMojo that checks if any errors have occurred and that fails the build if any errors occurred.
The BuildImageMojo now reports errors when one of the image builds fails. These errors can be picked up by the verify task to fail the build.
When pushing an image fails, it fails the build.
When starting a container fails, log a plugin error.
With normal execution, assume no plugin errors are logged.
VerifyMojo now logs which goals have caused errors.
Added the verify goal to all integration tests and fixed the simple-it Dockerfile so that nginx is working again.
Add verify goal to readme.
Merge pull request #16 from wouterd/feature/verify-mojo

Verify mojo added to fail the build when errors occur in other Mojos
Added "tag-images" goal to plugin

Added tagging as a "deploy" goal as a means to "release" an image that
can/should be used in a release/production environment. Images are
explicitly listed (referencing their "build" ids), given one or more
tags and optionally "pushed" with those tags.

Updated README.

While here:

- slight bug fix to ImageDescriptor to allow "." and "-" in tags e.g.
"ubuntu:14.04"
- it maven test needs to run "deploy" phase, but actual maven artifact
deployment needs to disabled in each POM.
- slight refactoring using Optional<> for different ImageDescriptor
members for clarity/consistency
Propagate simple-it's mended Dockerfile to other its

(And merge latest upstream)
Unit tests for new tag-mojo related classes.
Updated README to reflect swapping of phases between push and tag.