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
```
This makes it easier for new and experienced users to run cdist with higher
verbosity levels, both to know that things are working as expected and to debug
issues.
Documentation has been modified accordingly and default behaviour is not
changed.
CDIST_ORDER_DEPENDENCY now defines type order dependency context.
cdist (emulator) maintains global state variables, as files,
order_dep_state and typeorder_dep, and per object state variable,
as file, typeorder_dep.
If order_dep_state exists then this defines that order dependency is
turned on.
If order_dep_state does not exist then order dependency is turned off.
If order dependency is on then objects created after it is turned on are
recorded into:
* global typeorder_dep, in case of init manifest
* object's typeorder_dep, in case of type's manifest.
If order dependency is on then requirement is injected, where object
created before current, is read from:
* global typeorder_dep, in case of init manifest
* object's typeorder_dep, in case of type's manifest.
Every time order dependency is turned off, typeorder_dep files are
removed, which means that type order list is cleared, context is
cleaned.
In the end cdist cleans after itself, i.e. mentioned files are removed.
When running type manifest is finished typeorder_dep file is removed.
When running config finishes global typeorder_dep and order_dep_state
files are removed.
Global type order recording is untouched.
Furthermore, for completeness, type order is now recorded for each object
too.
