ec: Fix return errors when not enough bricks

Changes introduced by this patch:

* Fix an incorrect error propagation when the state of the life
  cycle of a fop returns an error.

* Fix incorrect unlocking of failed locks.

* Return ENOTCONN if there aren't enough bricks online.

* In readdir(p) check that the fd has been successfully open by
  a previous opendir.

Change-Id: Ib44f25a1297849ebcbab839332f3b6359f275ebe
BUG: 1162805
Signed-off-by: Xavier Hernandez <xhernandez@datalab.es>
Reviewed-on: http://review.gluster.org/9098
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>