Add suport for checksum string verification

Some times it's necessary to verify if a given file is equaled to another file inside hdfs, it could happen when we are trying to verify if the file content is different from an older version of this file.

For that, we have to implement a method to check if a given string checksum is equaled to the checksum of a file inside hdfs and return a boolean.

For now, this issue doesn't relate to the generation of a cross filesystem checksum.