Factor out some common object creation
Refactor some future common test object creation
Fix non-test function name (nose discovered it)
Add PTR–range container test
Add PTR target test
Improve test docstring
Add PTR domain container test
Add PTR target IP-resemblence test

(Also fix another test's name.)
Add PTR static interface same IP test
Change some variable names
Clarify test by not drawing attention to target
Add duplicate IP test
Add PTR in dynamic range test
Factor out test_ctnr1 and some creation logic
Sort imports; remove unnecessary try–excepts
Use create_basic_dns_data in AddressRecord tests
Remove 'ptr' from some test names

... so that they're more consistent with our test name "convention".
Add AddressRecord same name test
Test AddressRecord–CNAME name conflict test
Change some double quotes to single quotes