travis: Run integration tests with and without valgrind on travis

Run one travis build with valgrind on legacy tests, off on new daemon
tests, and another build with the roles switched. Should also speed
this up a bit since we run in parallel.

.travis.yml

@@ -2,6 +2,10 @@ language: c
 dist: trusty
 sudo: true
 
+env:
+  - NOVALGRIND=1 NO_VALGRIND=0
+  - NOVALGRIND=0 NO_VALGRIND=1
+
 # Trusty (aka 14.04) is way way too old, so run in docker...
 script:
   - docker pull cdecker/lightning-ci > /dev/null