profiles/internal/rpc: more verror conversions and tests.

MultiPart: 2/2

Change-Id: Id0e77e55764b6df0116566ff5052b2056c418b40
diff --git a/profiles/internal/rpc/test/simple_test.go b/profiles/internal/rpc/test/simple_test.go
index bc653f4..c83ec25 100644
--- a/profiles/internal/rpc/test/simple_test.go
+++ b/profiles/internal/rpc/test/simple_test.go
@@ -29,6 +29,10 @@
 	return "pong", nil
 }
 
+func (s *simple) Echo(call rpc.ServerCall, arg string) (string, error) {
+	return arg, nil
+}
+
 func (s *simple) Source(call rpc.StreamServerCall, start int) error {
 	i := start
 	backoff := 25 * time.Millisecond