runtime: return a different bubble deadlock error when main goroutine is done

The synctest.Test function waits for all goroutines in a bubble to
exit before returning. If there is ever a point when all goroutines
in a bubble are durably blocked, it panics and reports a deadlock.

Panic with a different message depending on whether the bubble's
main goroutine has returned or not. The main goroutine returning
stops the bubble clock, so knowing whether it is running or not
is useful debugging information.

The new panic messages are:
	deadlock: all goroutines in bubble are blocked
	deadlock: main bubble goroutine has exited but blocked goroutines remain

Change-Id: I94a69e79121c272d9c86f412c1c9c7de57ef27ef
Reviewed-on: https://go-review.googlesource.com/c/go/+/679375
Auto-Submit: Damien Neil <dneil@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

0 files changed, 0 insertions, 0 deletions