Improved tests stability on travis 

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes (not on 2.2 with 5.3.3 due to a segmentation fault happening for other reasons)
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

Process pipe tests seem to be failing more often after we parallelised the build. It looks like sometimes there's an additional output generated (might be that other tests are interferring).

This PR makes sure that the problematic tests are run in a non-parallel mode. It also changes the "tty" group to "noparallel" to better reflect its intention.