grpcproxy: Disable fast fail on lease grant call to cluster
grpcproxy: Disable fast fail on lease grant call to cluster

Problem Observed
----------------

When there is no etcd process behind the proxy,
clients repeat resending lease grant requests without delay.
This behavior can cause abnormal resource consumption on CPU/RAM and
network.

Problem Detail
--------------

`LeaseGrant()` uses a bare protobuf client to forward requests.
However, it doesn't use `grpc.FailFast(false)`, which means the method returns
an `Unavailable` error immediately when no etcd process is available.
In clientv3, `Unavailable` errors are not considered the "Halt" error,
and library retries the request without delay.
Both clients and the proxy consume much CPU cycles to process retry requests.

Resolution
----------

Add `grpc.FailFast(false))` to `LeaseGrant()` of the `leaseProxy`.
This makes the proxy not to return immediately when no etcd process is
available. Clients will simply timeout requests instead.

cockroachdb/etcd,whuwxl/etcd,akauppi/etcd,gyuho/etcd,mqliang/etcd,li-ang/etcd,bluebreezecf/etcd,ajityagaty/etcd,vimalk78/etcd,lorneli/etcd,bluebreezecf/etcd,lorneli/etcd,heyitsanthony/etcd,bdarnell/etcd,mickep76/etcd,rnaveiras/etcd,glevand/coreos--etcd,sebrandon1/etcd,a-robinson/etcd,sinsharat/etcd,glevand/coreos--etcd,dannysauer/etcd,mickep76/etcd,rnaveiras/etcd,dannysauer/etcd,sinsharat/etcd,whuwxl/etcd,akauppi/etcd,etcd-io/etcd,rnaveiras/etcd,a-robinson/etcd,mkumatag/etcd,visheshnp/etcd,mqliang/etcd,joshix/etcd,cockroachdb/etcd,mqliang/etcd,YuleiXiao/etcd,ajityagaty/etcd,xiang90/etcd,fanminshi/etcd,etcd-io/etcd,fanminshi/etcd,etcd-io/etcd,mkumatag/etcd,ajityagaty/etcd,YuleiXiao/etcd,gyuho/etcd,mkumatag/etcd,xiang90/etcd,joshix/etcd,coreos/etcd,bdarnell/etcd,sebrandon1/etcd,vimalk78/etcd,visheshnp/etcd,li-ang/etcd,coreos/etcd,heyitsanthony/etcd