add block handler to handle block files on different under file systems[Tachyon-33][SubTask 1]

details are on Tachyon's JIRA
BlockHandler is used to read and write block files on different under file systems, currently local file system is realized.
It doesn't throw, but how do I know it failed?  Java files tend to return false rather than IO.  So this method should either throw an exception or return a boolean (boolean is nice).