Indicate that the build was successful after a build error.

Prior to this change if a build errored it was not possible to know from
the console if that issue has been corrected. This forced us to stop &&
restart the server to get feedback (even though it had likely already
been fixed).

This change adds a "Build successful." message when the build had
previously errored (the stack was already printed to the screen), and is
now built properly.

@danmcclain / @rjackson
Merge pull request #412 from rjackson/show-rebuild-successful

Indicate that the build was successful after a build error.
Create own tree for tests files and avoid testing files on ENV=production [fixes #409].
Merge pull request #424 from abuiles/test-files

Create own tree for tests files and avoid testing files on ENV=productio...
Add `ember test`.