Working with Backends.
Get backend class by name.
The backend string is the full path to a backend class, e.g.:
"carrot.backends.pyamqplib.Backend"
If the name does not include “.” (is not fully qualified), the alias table will be consulted.
S.rpartition(sep) -> (head, sep, tail)
Search for the separator sep in S, starting at the end of S, and return the part before it, the separator itself, and the part after it. If the separator is not found, return two empty strings and S.