Improve warning when collector is paused by duplicate process

[seanlinsley]

The collector pause warning may have made sense to us internally, but it doesn't help users identify the issue on their own. This PR rewords it to be very clear about how to resolve the issue, though it removes the "processing disabled" part to avoid making the message too long.

In passing, this PR also updates the test run summary to use simpler wording.

[msakrejda]

Nice, thanks for clarifying this. We don't use periods elsewhere in similar messages, so I proposed a rewording to just use a colon. A semicolon or a different rewording could also work.