travis: move make -j flag out of script

Because global environment variables can be overridden when .travis.yml
is processed by the docker-travis target, the effect of this patch is
that docker-travis now obeys the "J=n" option.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>

.travis.yml

@@ -46,6 +46,7 @@ notifications:
 env:
   global:
     - TEST_CMD="make check"
+    - MAKEFLAGS="-j3"
   matrix:
     - CONFIG=""
     - CONFIG="--enable-debug --enable-debug-tcg --enable-trace-backends=log"
@@ -64,7 +65,7 @@ before_install:
 before_script:
   - ./configure ${CONFIG}
 script:
-  - make -j3 && ${TEST_CMD}
+  - make ${MAKEFLAGS} && ${TEST_CMD}
 matrix:
   include:
     # Test with CLang for compile portability