<yum-validator> Rejigger scripts and conf files for packaging

Created `yumvalidator` package under `yum-validator` app directory

Created `yum-validator/etc` directory to hold config data

Added `RepoDBError` for signaling problems instantiating a `RepoDB`

Added code to catch `RepoDBError` during `OpenShiftYumValidator`
instantiation and bail, since no repo data means no worky

Moved default repository data from `yumvalidator/repo_db.py` to `etc/repos.ini`

Updated `repo_db.py` to check `/etc/yum-validator/repos.ini` and
`./etc/repos.ini` for default repository data, and raise `RepoDBError`
if file can't be found or loaded.

Updated modules with new `yumvalidator` package references

Added some more missing docstrings

Added symlink from `yum-validator/beta2.ini` to `yum-validator/etc/beta2.ini` to prevent breaking https://access.redhat.com/site/articles/531473