docs: fix simple typo, untill -> until

DNS resolution errors were previously not retriable, this commit allows it by changing the value returned when the DNS resolution fails.

There is a small typo in kazoo/recipe/queue.py.

Should read `until` rather than `untill`.

Without this patch, a single select event is processed by iteration in
the 'ConnectionHandler' event loop.

In a scenario where the client issues a large number of async requests
with an important amplification factor, e.g. 'get_children_async' on a
large node, it is possible for the 'select' operation to almost always
return a "response ready" socket--as the server is often able to
process, serialize and ship a new reponse while Kazoo processes the
previous one.

That response socket often (always?) ends up at the beginning of the
list returned by 'select'.

As only 'select_result[0]' is processed in the loop, this can cause
the client to ignore the "request ready" FD for a long time, during
which no requests or pings are sent.

In effect, asynchronously "browsing" a large tree of nodes can stretch
that duration to the point where it exceeds the timeout--causing the
client to lose its session.

This patch considers both descriptors after 'select', and also
arranges for pings to be sent in case it encounters an "unending"
stream of responses to requests which were sent earlier.

This adds a simple recovery path in case an SSL connection receives
an SSL_WANT_READ or WRITE error.  Either error can occur while
reading or writing.  The error indicates that the underlying
operation should be retried after the socket is once again readable
or writable (per the error code).

Closes #618

Co-authored-by: James E. Blair <jeblair@redhat.com>

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