tests were sensitive to additional log lines appearing in the log
causing the search to come empty handed.

instead of just looking for the n last log lines, capture the log lines
before performing the action, and then search from that offset.

i.e. don't start the search from scratch hitting the used ones again.
this will also reduce the likelihood of collisions (if there are any
left) by increasing the time until we re-use a port we did use in the
past.

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.

now that replica can read rdb directly from the socket, it should avoid exiting
on short read and instead try to re-sync.

this commit tries to have minimal effects on non-diskless rdb reading.
and includes a test that tries to trigger this scenario on various read cases.

The implementation of the diskless replication was currently diskless only on the master side.
The slave side was still storing the received rdb file to the disk before loading it back in and parsing it.

This commit adds two modes to load rdb directly from socket:
1) when-empty
2) using "swapdb"
the third mode of using diskless slave by flushdb is risky and currently not included.

other changes:
--------------
distinguish between aof configuration and state so that we can re-enable aof only when sync eventually
succeeds (and not when exiting from readSyncBulkPayload after a failed attempt)
also a CONFIG GET and INFO during rdb loading would have lied

When loading rdb from the network, don't kill the server on short read (that can be a network error)

Fix rdb check when performed on preamble AOF

tests:
run replication tests for diskless slave too
make replication test a bit more aggressive
Add test for diskless load swapdb

Uses ANSI "default background" color code after closing tests
so any non-black terminals don't remain polluted.

Fixes #1649
Closes #1912

The function will only return ports that have also port+10000 free, so
that Redis Cluster instances can be executed at the returned port.

Some inline test moved into server_is_up procedure.
Also find_available_port was moved into util since it is going
to be used for the Sentinel test as well.

A new stress test was added to stress test the code converting a ziplist
into an hash table.

In this commit also randomValue helper function was modified to also
return negative values.

wait_for_condition is now used instead of the usual "after 1000" (that
is the way to sleep in Tcl). This should avoid to find the replica in
a state where it is loading the RDB in memory, returning -LOADING error.

This test used to fail when running the test over valgrind, due to the
added latencies.

Commit 33e1db36 modified the name of a
few INFO fields. This commit changes the Redis test to account for this
changes.

Due to a change in the format of the bug report in case of crash of
failed assertion the test suite was no longer able to properly log it.
Instead just a protocol error was logged by the Redis TCL client that
provided no clue about the actual problem.

This commit resolves the issue by logging everything from the first line
of the log including the string REDIS BUG REPORT, till the end of the
file.

better random dataset creation function in test. master-slave replication test now is able to save the two datasets in CSV when an inconsistency is detected.

print warnings in redis log when a test raises an exception (very likely to be caused by something like a failed assertion)