kvdb/etcd: remove context.TODO() from test helpers

We want `context.TODO()` to be high signal in the code-base. It should
signal clearly that work is required to thread parent context through to
the call-site. So to keep the signal-to-noise ratio high, we remove any
context.TODO() calls from tests since these will never need to be
replace by a parent context.

After this commit, there is only a single context.TODO() left in the
code-base.

kvdb/etcd/walletdb_interface_test.go

@@ -15,5 +15,5 @@ import (
 func TestWalletDBInterface(t *testing.T) {
 	f := NewEtcdTestFixture(t)
 	cfg := f.BackendConfig()
-	walletdbtest.TestInterface(t, dbType, context.TODO(), &cfg)
+	walletdbtest.TestInterface(t, dbType, context.Background(), &cfg)
 }