make --job a bit smarter when uploading test reports

[jfgrimm]

Currently, -r --job --from-pr will generate one test report per submitted job, and post that as a comment on the PR. Particularly when building something depending on a new toolchain, this can spawn a lot of jobs (resulting in a lot of separate comments) for a single PR.

[boegel]

@jfgrimm That tells me that we should essentially disable --robot when --from-pr is combined with --job?

Or perhaps only if --upload-test-report is also used?

[branfosj]

Definitely we should disable it when --upload-test-report is used.

When just --from-pr is used with --job it allows someone to build up the stack of software up to that PR using the job functionality.