Don't build packages for PRs on travis, run only tests

[printercu]

Some additional changes:

• Remove deploy to 1_9 repo
• Add deploy to 2_4 repo
• Remove packaging for fedora26, fedora27
• Add packaging for el8, fedora31, ubuntu-eoan
• Run tests against tarantool 2.2 and 2.4 (with allow_failure: true).

[Gerold103]

CI is in github now instead of Travis.