Add support for retrying writes after transient server errors.
Add support for retrying writes after transient server errors.

mjg59/mantle,marineam/mantle,glevand/coreos--mantle,glevand/coreos--mantle,dm0-/mantle,mjg59/mantle,quantum/coreos-mantle,crawford/mantle,pbx0/mantle,dm0-/mantle,quantum/coreos-mantle,marineam/mantle,mischief/mantle,mischief/mantle