All changes are needed to eliminate sporadic fails when testing is run
with, say, 30 parallel jobs.

First, replication_connect_timeout is increased to 30 seconds. This
parameter doesn't change meaning of the test cases.

Second, increase replication_timeout from 0.01 to 0.03. We usually set
it to 0.1 in tests, but a duration of the gh-3160 test case ('Send
heartbeats if there are changes from a remote master only') is around
100 * replication_timeout seconds and we don't want to make this test
much longer. Runs of the test case (w/o other ones that are in
replication/mics.test.lua) in 30 parallel jobs show that 0.03 is enough
for the gh-3160 case to pass stably and hopefully enough for the
following test cases too.