cluster/afr: implement self-heal using syncops

Change-Id: I96478522e3f2c5516b92a85f409a2503201f0fc0
Signed-off-by: Anand Avati <avati@redhat.com>
cluster/afr: improve lookup() robustness

Signed-off-by: Anand Avati <avati@redhat.com>