The green socket module seemed to have only blocking DNS resolution
methods even with dnspython installed which is inconsistent with the
documentation.
This patch has a few consequences:
* an import cycle is eliminated
* if an import cycle reappears here it'll be visible
Note: eliminating the import cycle revealed an issue related to monkey
patching and the way we perform greendns tests (the test failures were
already present on Python 3.5[1] as that version has some import cycle
handling changes). The failures look like this:
======================================================================
FAIL: test_query_ans_types (tests.greendns_test.TestHostsResolver)
----------------------------------------------------------------------
Traceback (most recent call last):
File "/Users/kuba/projects/eventlet/tests/greendns_test.py", line 97, in test_query_ans_types
assert isinstance(ans, greendns.dns.resolver.Answer)
AssertionError
======================================================================
FAIL: test_query_unknown_no_raise (tests.greendns_test.TestHostsResolver)
----------------------------------------------------------------------
Traceback (most recent call last):
File "/Users/kuba/projects/eventlet/tests/greendns_test.py", line 129, in test_query_unknown_no_raise
assert isinstance(ans, greendns.dns.resolver.Answer)
AssertionError
This issue will be addressed in a separate commit.
This patch is contributed by Smarkets Limited.
[1] https://github.com/eventlet/eventlet/issues/267
861d684399