.travis.yml: reduce number of targets built while disabling things

This build keeps timing out on Travis and it's unlikely including the
additional guest front-ends will catch any failures in the fallback
code.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Acked-by: Stefano Garzarella <sgarzare@redhat.com>
Reviewed-by: Wainer dos Santos Moschetta <wainersm@redhat.com>

.travis.yml

@@ -107,7 +107,7 @@ matrix:
 
 
     - env:
-        - CONFIG="--disable-linux-aio --disable-cap-ng --disable-attr --disable-brlapi --disable-libusb --disable-user --disable-replication"
+        - CONFIG="--disable-linux-aio --disable-cap-ng --disable-attr --disable-brlapi --disable-libusb --disable-replication --target-list=${MAIN_SOFTMMU_TARGETS}"
 
 
     # Module builds are mostly of interest to major distros