fix bug of failing to write to tachyon when speculation execution is on
change the sequence of writing files
format modification
solve filenotexsitexception when table has an empty partition
clean code for writeColumnPartition
merge PR327
change Tachyon version to 0.5.0
some format fix
Merge pull request #339 from shimingfei/tachyon-table-write

FileAlreadyExistException when writing tachyon table