Check whether O_DIRECT is supported to iflag and oflag separately

The problem is when this is used for volume clear and the clear method
specifies use of the 'zero' option (/dev/zero) setting iflag direct is
not a valid option for that input file, but oflag direct is a valid
option for output file, so we should check iflag and oflag separately.

Change-Id: I4b627e95b68d56e3011cddc577c62fad0c384dba
Close-Bug: 1318748