Handling Invalid argument iflag=direct in dd

Handling Invalid argument iflag=direct in dd

During volume/snapshot create/delete operations,
dd command is used to clear contents of disk.

Before invoking dd, it is checked if iflag=direct
supports dd or not by executing dd command with
iflag=direct and if=/dev/zero combination.
But this always results in invalid argument
error.

Handling for this argument is done to eliminate
unnecessary call to dd command when it is used
with iflag=direct and if=/dev/zero combination
to check if this argument supports dd or not.

Closes-Bug: #1270362

Change-Id: Ic6dd029ca1a339076e491c38ef3c69315497f189