convert should use default value when CVS_RSH is not set, that value

being 'ssh'.

hgext/convert/cvs.py

@@ -179,7 +179,7 b' class convert_cvs(converter_source):'
 
         if conntype != "pserver":
             if conntype == "rsh":
-                rsh = os.environ.get("CVS_RSH" or "rsh")
+                rsh = os.environ.get("CVS_RSH") or "ssh"
                 if user:
                     cmd = [rsh, '-l', user, host] + cmd
                 else: