raise a specific CacheManagerException from cache

Instead of reraising Exception with an added
msg, raise a specific exception here, and pass
original exception msg along.

Remove empty catch and reraise of RestlibException,
it just confuses stack traces.
Don't reraise exception by name in repolib

Add test cases for it.
Dont reraise exceptions by name, just raise.
Dont reraise exception by, just reraise