quick-read: implement qr_writev
quick-read: implement qr_writev

- writev on any fd opened on a file invalidates the cache stored during lookup

Signed-off-by: Anand V. Avati <6a1810c170bd423868ce2e225ecea39d80cade0f@dev.gluster.com>

Kaushikbv/Gluster,Kaushikbv/Gluster,Kaushikbv/Gluster