travis-ci: Optimize and rearrange .travis.yml

- Remove redundant 'os: linux', 'compiler: gcc' tags.
- Order jobs: x86_64 builds, analysers, other arches, other OSes.
- Mark openssl-master build as 'allow_failures' for PRs.
- Build all jobs against 'OpenSSL_1_1_1-stable' by default.
- Do not include 'linux/arch' in the job name, because Travis show
  them already.
- Split name by ' | ' instead of '/' so it's easier to understand.