travis: Automatically recheck failed tests.

This should make the automatic testsuite more reliable on Travis.  It's
better to fix tests to be more reliable, of course, but in practie it's
difficult to make all of them 100% reliable.

Signed-off-by: Ben Pfaff <blp@ovn.org>
Acked-by: Andy Zhou <azhou@ovn.org>

.travis/build.sh

@@ -99,7 +99,7 @@ else
 fi
 
 if [ "$TESTSUITE" ] && [ "$CC" != "clang" ]; then
-    if ! make distcheck; then
+    if ! make distcheck RECHECK=yes; then
         # testsuite.log is necessary for debugging.
         cat */_build/tests/testsuite.log
         exit 1