make system constants configurable as vars.

This configurability is unlocked through the `testground`
build tag, which Project Oni will uses.

Changes in the usage places of these relaxed constants
were required due to the fact that Golang constants are
untyped, but vars aren't.

Read https://blog.golang.org/constants for more info.

markets/storageadapter/client.go

@@ -330,7 +330,7 @@ func (c *ClientNodeAdapter) OnDealSectorCommitted(ctx context.Context, provider
 		}
 	}
 
-	if err := c.ev.Called(checkFunc, called, revert, build.MessageConfidence+1, build.SealRandomnessLookbackLimit, matchEvent); err != nil {
+	if err := c.ev.Called(checkFunc, called, revert, int(build.MessageConfidence+1), build.SealRandomnessLookbackLimit, matchEvent); err != nil {
 		return xerrors.Errorf("failed to set up called handler: %w", err)
 	}
 

markets/storageadapter/provider.go

@@ -321,7 +321,7 @@ func (n *ProviderNodeAdapter) OnDealSectorCommitted(ctx context.Context, provide
 
 	}
 
-	if err := n.ev.Called(checkFunc, called, revert, build.MessageConfidence+1, build.SealRandomnessLookbackLimit, matchEvent); err != nil {
+	if err := n.ev.Called(checkFunc, called, revert, int(build.MessageConfidence+1), build.SealRandomnessLookbackLimit, matchEvent); err != nil {
 		return xerrors.Errorf("failed to set up called handler: %w", err)
 	}