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
```
For a good reason, __package_apt doesn't install recommended packages as
default. But the option --install-recommends comes handy if you want to
install a package where you want to install all recommended packages
(and not to install all of them separately).
Also, the manpage now explains that the type won't install recommended
packages by default.
