travis: Include testsuite.log on failure.

Acked-by: Thomas Graf <tgraf@noironetworks.com>
Signed-off-by: Ben Pfaff <blp@nicira.com>
travis: Allow testsuite to run with GCC or Clang.

I don't see why the testsuite is supported only with GCC.

Acked-by: Thomas Graf <tgraf@noironetworks.com>
Signed-off-by: Ben Pfaff <blp@nicira.com>