Travis: Allow failable build with upstream opam repo

Signed-off-by: Frederico Mazzone <[email protected]>

Author: Frezzle

.travis.yml

@@ -5,6 +5,11 @@ sudo: true
 env:
   global:
     - PACKAGE=xapi-idl
-    - BASE_REMOTE=git://github.com/xapi-project/xs-opam
-  matrix:
     - OCAML_VERSION=4.02
+  matrix:
+    - BASE_REMOTE=git://github.com/xapi-project/xs-opam
+    - EXTRA_REMOTES=git://github.com/xapi-project/xs-opam
+matrix:
+  fast_finish: true
+  allow_failure:
+    - env: OCAML_VERSION=4.02 PACKAGE=xapi-idl EXTRA_REMOTES=git://github.com/xapi-project/xs-opam