Add Confd client to the Haskell code base

Add Confd client to the Haskell code base

The client queries all the master candidates in parallel, until the minimum
number of replies, defined in the constant file, is received.
A timeout prevents the waiting from being of indefinite length.

The reply to be returned to the function that made the query is decided
according to the Confd design document.

Signed-off-by: Michele Tartara <mtartara@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>