ENH: Func to check which pool a guest belongs.
ENH: Func to check which pool a guest belongs.

Added function __get_pool_for_guest to check where a guest is hosted.
Then the pool is ran against __verify_valid_pool and then ran against
__verify_valid_guest. This is a matter of thoroughness  as in the user
facing functions also get checked again, especially when user input for
pool/guest name is optional.

chyves/chyves