Adds back experiments ndt.iupui and mlab.neubot (#321)

Removing them breaks mlab-ns and the changes to accommodate this and make
mlab-ns still work are too many, and involve even some bugs in GMX. It's too
much work at the moment.

One practical effect this change has on supporting "minimal" sites with /28 and
/29 IPv4 prefixes is that now /28 sites will only support up to index 10, and
/29 sites will only support mask, ndt and ndt.iupui (without revtr). Both of
these outcomes is probably just fine for v1 of minimal sites.

experiments.jsonnet

@@ -14,6 +14,11 @@ local default = {
     cloud_enabled: true,
     name: 'ndt',
   },
+  default {
+    index: 2,
+    name: 'ndt.iupui',
+    cloud_enabled: true,
+  },
   default {
     index: 3,
     name: 'revtr',
@@ -46,6 +51,10 @@ local default = {
     index: 10,
     name: 'neubot',
   },
+  default {
+    index: 10,
+    name: 'neubot.mlab',
+  },
   default {
     index: 11,
     name: 'demo11',