group-virt: Change profile to include remote-dio and exclude posix-aio.

remote-dio enables filtering O_DIRECT in the client xlator. This has been
found to be useful for improving performance when there are multiple VMs
talking to an image store.

Aggregated throughput results for a single thread iozone run from multiple VMs
and a single host can be seen below:

-------------------------------------------------
No. of VMs |   remote-dio on  |   remote-dio off |
-------------------------------------------------
       2   |     400 MB/s     |    202 MB/s      |
       4   |     650 MB/s     |    410 MB/s      |
--------------------------------------------------

posix-aio has not been found to improve performance consistently with VM image
workload. Hence not including that in the default virt profile.

Change-Id: I592f68b95a955036f1a985352d2f4950ced1deef
BUG: 907301
Signed-off-by: Vijay Bellur <vbellur@redhat.com>
Reviewed-on: http://review.gluster.org/4460
Reviewed-by: Anand Avati <avati@redhat.com>
Tested-by: Anand Avati <avati@redhat.com>