permission bug fix

Hadoop only accepts permissions with values between 0 and 777.
fix return value during write

FUSE expects the number of written bytes after a write, but it got 0 on success.
add dummy methods to support write

The methods:
* webhdfs_fuse_utime()
* webhdfs_fuse_utimens()
* webhdfs_fuse_truncate()
* webhdfs_fuse_ftruncate()