Reenable Travis CI.

[kennytm]

1. Merged the two original .travis.yml inside the subpackages to the top level.

2. Fixed several issues which prevented Travis from passing:

   1. Disabled site/tests/lib.rs due to site/tests/lib.rs is outdated #165. (Thus currently cargo test does absolutely nothing 🤷‍)
   2. Fixed the workspace issue when trying to run collector/check-benchmarks.sh.
   3. Repurpose collector/check-benchmarks.sh for Travis checking only (removed set -x and added some travis_fold). I think for development most people would run the collector directly.

[Mark-Simulacrum]

Will collector still be part of the workspace with the current changes?

[kennytm]

Yes. (I think this may be a misfeature of Cargo.)

https://travis-ci.org/rust-lang-nursery/rustc-perf/jobs/293550642#L861

[Mark-Simulacrum]

So we'd be depending on a bug, sort of?

[kennytm]

@Mark-Simulacrum Yeah... the bug seems to be rust-lang/cargo#4089. There is a fix at rust-lang/cargo#4297 but it has been sitting there for 3 months? Perhaps we could hold this off until the bug is fixed on nightly.

Or we could remove the top-level workspace.

[Mark-Simulacrum]

Hm, it looks like maybe it was fixed by rust-lang/cargo#4594?

[kennytm]

@Mark-Simulacrum Nope, the description states

This is the first step of the fix, that's only a codemod to put together the relevant parts : workspace.members, workspace.excludes, and the root_dir (where members and excludes are relative to). There's no logic change in this PR to keep review easier.