.travis.yml: Exclude openrd platforms

The openrd platforms are currently orphaned, and are constantly on-edge
or overflowing their binary limit.  Exclude them from travis for now.

Cc: Vagrant Cascadian <vagrant@debian.org>
Cc: Chris Packham <judge.packham@gmail.com>
Signed-off-by: NTom Rini <trini@konsulko.com>

.travis.yml

@@ -195,7 +195,7 @@ matrix:
         - BUILDMAN="sandbox x86"
           TOOLCHAIN="x86_64"
     - env:
-        - BUILDMAN="kirkwood"
+        - BUILDMAN="kirkwood -x openrd"
     - env:
         - BUILDMAN="mvebu"
     - env: