apparently when running tests in parallel (the default of --clients 16),
there's a chance for two tests to use the same port.
specifically, one test might shutdown a master and still have the
replica up, and then another test will re-use the port number of master
for another master, and then that replica will connect to the master of
the other test.
this can cause a master to count too many full syncs and fail a test if
we run the tests with --single integration/psync2 --loop --stop
see Probmem 2 in #7314
* Introduce a connection abstraction layer for all socket operations and
integrate it across the code base.
* Provide an optional TLS connections implementation based on OpenSSL.
* Pull a newer version of hiredis with TLS support.
* Tests, redis-cli updates for TLS support.
The test now runs in a self-contained directory.
The general abstractions to run the tests in an environment where
mutliple instances are executed at the same time was extrapolated into
instances.tcl, that will be reused to test Redis Cluster.
