Now that we are using `pytest`, there is no need for a custom decorator
because we can use `pytest.mark.skipif()`.

This makes the code significantly simpler. In particular, dropping the
custom `@kafka_versions()` decorator is necessary because it uses
`func.wraps()` which doesn't play nice with `pytest` fixtures:
- https://github.com/pytest-dev/pytest/issues/677
- https://stackoverflow.com/a/19614807/770425

So this is a pre-requisite to migrating some of those tests to using
pytest fixtures.

Remove unused import, whitespace, etc. No functional changes, just
cleaning it up so the diffs of later changes are cleaner.

More attempts to address heartbeat timing issues in consumers, especially with the iterator interface. Here we can reduce the `client.poll` timeout to at most the retry backoff (typically 100ms) so that the consumer iterator interface doesn't block for longer than the heartbeat timeout.

socket.SOCK_STREAM is platform specific and on some
platforms (most notably on Linux on MIPS) does not
equal 1; so it's better to use the constant where
appropriate.

This change fixes the tests on my MIPS32 LE machine.

Signed-off-by: Ivan A. Melnikov <iv@altlinux.org>

This splits the `_find_coordinator_id()` method (which is blocking) into
request generation / response parsing methods.

The public API does not change. However, this allows power users who are
willing to deal with risk of private methods changing under their feet
to decouple generating the message futures from processing their
responses. In other words, you can use these to fire a bunch of requests
at once and delay processing the responses until all requests are fired.

This is modeled on the work done in #1845.

Additionally, I removed the code that tried to leverage the error
checking from `cluster.add_group_coordinator()`. That code had changed
in #1822, removing most of the error checking... so it no longer adds
any value, but instead merely increases complexity and coupling.

the new consumer is now the standard consumer, so they dropped the `new_` from the anchor

Previously the `sasl_kerberos_domain_name` was missing from the Admin
client. It is already present in the Consumer/Producer, and in all three
cases gets transparently passed down to the client.

Updated to include SASL_PLAINTEXT and SASL_SSL as options for security_protocol.