REQ-627 setup Travis for feature branch

This causes Travis to use branch REQ-627 of the xs-opam-based Travis
build.

Signed-off-by: Christian Lindig <[email protected]>

Author: lindig

.travis.yml

@@ -9,4 +9,5 @@ env:
     - PINS="xapi-idl:."
     - DISTRO="debian-unstable"
     - OCAML_VERSION="4.07"
+    - BASE_REMOTE_BRANCH="REQ-627"
     - BASE_REMOTE="https://github.com/xapi-project/xs-opam.git"