This commit implements FUSE_SETATTR command. When a system call modifies
the metadata of a regular file or a folder by chown(2), chmod(2),
truncate(2), utime(2), or utimes(2), they should be translated to
corresponding FUSE_SETATTR command and sent to the FUSE server.
Fixes #3332
According to Linux 4.4's FUSE behavior, the flags and fh attributes in
FUSE_GETATTR are only used in read, write, and lseek. fstat(2) doesn't
use them either. Add tests to ensure the requests sent from FUSE module
are consistent with Linux's.
Updates #3655
