test: fix flaky feedback_daemon_metrics test

The patch fixes two mistakes that were made while writing the test.
Firstly, we should replace metrics module with an empty table before
every test case - otherwise, metrics can be collected before the test.
Secondly, all attempts to check if a required amount of metrics was
collected is pointless, even with margin - some environments are
incredibly slow. So let's check if some metrics were collected, and check
if there are not too many of them.

Also, the patch increases some timeouts to minimize the probability of
fail due to slow environment.

Follows up #8192
Closes tarantool/tarantool-qa#312

NO_CHANGELOG=test
NO_DOC=test

(cherry picked from commit d187b142)