.travis.yml: minor optimizations:
.travis.yml: minor optimizations:

- make 'pip install --user cpp-coveralls' conditional;
- limit no-stdio to single build per operating environment;
- omit enable-asan duplicate;

Reviewed-by: Richard Levitte <5fb523282dd7956571c80524edc2dccfa0bd8234@openssl.org>

openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl