lib: Add test.V23InitWithNamespace

Many tests use endpoints instead of names out of laziness.  This makes
it nearly zero cost to use names which makes the test code more realistic
and cleaner.

This introduces new dependencies for external tests in other repos, so
several .godepcop files were modified.

MultiPart: 2/3

Change-Id: I3e976b6245ee2e92611747336b9f516844510c6b
diff --git a/.godepcop b/.godepcop
index abc6885..7796b92 100644
--- a/.godepcop
+++ b/.godepcop
@@ -10,6 +10,7 @@
 
   <!-- Relax the rule for external tests, but keep a curated list rather than
        allowing a blanket "..." to avoid adding unwanted dependencies. -->
+  <xtest allow="github.com/presotto/go-mdns-sd/..."/>
   <xtest allow="v.io/v23/..."/>
   <xtest allow="v.io/x/ref/..."/>
 </godepcop>