importlib has been a thing since Python 3.1, and imp has been deprecated since
3.4.
Insert random complaint here about not being able to use f-strings because they
were introduced in Python 3.6 and apparently we support Python 3.5 >,<.
Output diff before to after for ./bin/cdist-build-helper test (on heavy load):
```
1,2d0
< /usr/home/evilham/s/cdist/cdist/cdist/test/__main__.py:23: DeprecationWarning: the imp module is deprecated in favour of importlib; see the module's documentation for alternative uses
< import imp
72c70
< ERROR: cdisttesthost: __file/tmp/foobar requires object __file without object id. Defined at /tmp/tmp.cdist.test.g87lx7c8/tmp.cdist.test.6ramsakx
---
> ERROR: cdisttesthost: __file/tmp/foobar requires object __file without object id. Defined at /tmp/tmp.cdist.test.aqdf6vjz/tmp.cdist.test.jgv3udel
76c74
< test_nonexistent_type_requirement (cdist.test.emulator.EmulatorTestCase) ... ERROR: cdisttesthost: __file/tmp/foobar requires object __does-not-exist/some-id, but type __does-not-exist does not exist. Defined at /tmp/tmp.cdist.test.mma5j8ln/tmp.cdist.test.3zg4by4d
---
> test_nonexistent_type_requirement (cdist.test.emulator.EmulatorTestCase) ... ERROR: cdisttesthost: __file/tmp/foobar requires object __does-not-exist/some-id, but type __does-not-exist does not exist. Defined at /tmp/tmp.cdist.test.t8d6ockr/tmp.cdist.test.uimxurg9
86c84
< test_initial_manifest_environment (cdist.test.manifest.ManifestTestCase) ... VERBOSE: cdisttesthost: Running initial manifest /tmp/tmp.cdist.test.uvid60ij/759547ff4356de6e3d9e08522b0d0807/data/conf/manifest/dump_environment
---
> test_initial_manifest_environment (cdist.test.manifest.ManifestTestCase) ... VERBOSE: cdisttesthost: Running initial manifest /tmp/tmp.cdist.test._cttcnrj/759547ff4356de6e3d9e08522b0d0807/data/conf/manifest/dump_environment
89c87
< test_type_manifest_environment (cdist.test.manifest.ManifestTestCase) ... VERBOSE: cdisttesthost: Running type manifest /tmp/tmp.cdist.test.k1i2onpb/759547ff4356de6e3d9e08522b0d0807/data/conf/type/__dump_environment/manifest for object __dump_environment/whatever
---
> test_type_manifest_environment (cdist.test.manifest.ManifestTestCase) ... VERBOSE: cdisttesthost: Running type manifest /tmp/tmp.cdist.test.ukr7lrzd/759547ff4356de6e3d9e08522b0d0807/data/conf/type/__dump_environment/manifest for object __dump_environment/whatever
272c270
< Ran 225 tests in 44.457s
---
> Ran 225 tests in 43.750s
```
Because it currently only support IPv4. To implement this, it falls back
to IPv4 for backward compatibilty, but now supports rules for IPv6 and
both protocols at the same time.
