ec: Optimize read/write performance

This patch significantly improves performance of read/write
operations on a dispersed volume by reusing previous inodelk/
entrylk operations on the same inode/entry. This reduces the
latency of each individual operation considerably.

Inode version and size are also updated when needed instead
of on each request. This gives an additional boost.

This is a backport of http://review.gluster.org/8369/

Change-Id: I4b98d5508c86b53032e16e295f72a3f83fd8fcac
BUG: 1140844
Signed-off-by: Xavier Hernandez <xhernandez@datalab.es>
Reviewed-on: http://review.gluster.org/8746
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Jeff Darcy <jdarcy@redhat.com>
Reviewed-by: Dan Lambright <dlambrig@redhat.com>