hadoop-dist build to verify that shell profiles are created

HADOOP-14809 shows it's possible to break the shellprofile logic and not pick it up in our automated tests.

1. It is possible to use an ant task or two in a POM to explicitly look for the expected files and fail if any are missing.
2. Similarly, it is possible to count the # of shell profiles and fail if a new one arrives: that forces the providers of new modules to keep test #1 up to date