[TACHYON-65] Fix the listFiles method

[TACHYON-65] the ListFiles(path,recursive) function of
tachyon.master.MasterInfo class does not work well
Add the unit test for [TACHYON-65]
Merge pull request #350 from PasaLab/TACHYON-65

[TACHYON-65] Fix the listFiles method in tachyon.master.MasterInfo