Implemented filter_hash_of_hash

It can be used to filter hash of hashes retrieved from f.e. hiera.

Example:
filter_hash_of_hash({'a'=> {'c' => 2, 'd' => 1},'b'=> {'c'=> 2, 'd'=> 2}}, {'c' => 2})
Would result in: {'a'=> {'c' => 2, 'd' => 1},'b'=> {'c'=> 2, 'd'=> 2}}

filter_hash_of_hash({'a'=> {'c' => 2, 'd' => 1},'b'=> {'c'=> 2, 'd'=> 2}}, {'c' => 2, 'd' => 1})
Would result in: {'a'=> {'c' => 2, 'd' => 1}}

Change-Id: Iaa6670d8370464e1cf93a168b88f49f7bfac3184