travis-ci: Fix quietness of building of openssl

No need for `build.log' as `make -s' will output any failure.

Also, redirection was broken anyway since splitting make into two makes
with separate `-j' and install phase.

Add `travis_wait' to make traves not time-out on slow arches. Reference:
  https://docs.travis-ci.com/user/common-build-problems/#build-times-out-because-no-output-was-received

Fixes: c38ec7587 ("travis: speed up Travis build")