Run dejagnu's runtest with -a option to prevent travis timeouts after 10min

.travis.yml

diff --git a/.travis.yml b/.travis.yml
index 7ca4c2c..8915ef9 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -31,5 +31,5 @@
   - ./configure ${HOST+--host=$HOST} ${CONFIGURE_OPTIONS}
   - make
   - make dist
-  - make check ${RUNTESTFLAGS+RUNTESTFLAGS="$RUNTESTFLAGS"}
+  - make check RUNTESTFLAGS="-a $RUNTESTFLAGS"
   - cat */testsuite/libffi.log