rpc: use gRPC enforced minimum keepalive timeout

Before this commit we'd experience the following annoying log message from gRPC
every time we create a new connection telling us that our setting is being
ignored.

```
Adjusting keepalive ping interval to minimum period of 10s
```

Release note: None

pkg/rpc/context_test.go

@@ -980,7 +980,7 @@ type grpcKeepaliveTestCase struct {
 func grpcRunKeepaliveTestCase(testCtx context.Context, c grpcKeepaliveTestCase) error {
 	var cKeepalive keepalive.ClientParameters
 	if c.cKeepalive {
-		cKeepalive = clientTestingKeepalive
+		cKeepalive = clientKeepalive
 	}
 	var sKeepalive keepalive.ServerParameters
 	if c.sKeepalive {

pkg/rpc/keepalive.go

@@ -17,16 +17,22 @@ import (
 	"google.golang.org/grpc/keepalive"
 )
 
+// 10 seconds is the minimum keepalive interval permitted by gRPC.
+// Setting it to a value lower than this will lead to gRPC adjusting to this
+// value and annoyingly logging "Adjusting keepalive ping interval to minimum
+// period of 10s". See grpc/grpc-go#2642.
+const minimumClientKeepaliveInterval = 10 * time.Second
+
 // To prevent unidirectional network partitions from keeping an unhealthy
 // connection alive, we use both client-side and server-side keepalive pings.
 var clientKeepalive = keepalive.ClientParameters{
 	// Send periodic pings on the connection.
-	Time: base.NetworkTimeout,
+	Time: minimumClientKeepaliveInterval,
 	// If the pings don't get a response within the timeout, we might be
 	// experiencing a network partition. gRPC will close the transport-level
 	// connection and all the pending RPCs (which may not have timeouts) will
 	// fail eagerly. gRPC will then reconnect the transport transparently.
-	Timeout: base.NetworkTimeout,
+	Timeout: minimumClientKeepaliveInterval,
 	// Do the pings even when there are no ongoing RPCs.
 	PermitWithoutStream: true,
 }
@@ -48,13 +54,6 @@ var serverEnforcement = keepalive.EnforcementPolicy{
 	PermitWithoutStream: true,
 }
 
-// These aggressively low keepalive timeouts ensure that tests which use
-// them don't take too long.
-var clientTestingKeepalive = keepalive.ClientParameters{
-	Time:                200 * time.Millisecond,
-	Timeout:             300 * time.Millisecond,
-	PermitWithoutStream: true,
-}
 var serverTestingKeepalive = keepalive.ServerParameters{
 	Time:    200 * time.Millisecond,
 	Timeout: 300 * time.Millisecond,