dispatch_test: use the NM tests timeouts

This commit makes the dispatch_test use the same timeouts that network manager tests. We do that because the old values appear to be too small for our heavy loaded CI machines, leading to spurious failures on them. The network manager tests are much more stable in this situation and they use somewhat larger timeout values.

We use a smaller connection timeouts for the tests which are expected to timeout to not wait for too long.

Closes #4434 (closed)