Configuration files in system tests which require some variables (e.g.
port numbers) filled in during test setup, can now use jinja2 templates
when `jinja2` python package is available.
Any `*.j2` file found within the system test directory will be
automatically rendered with the environment variables into a file
without the `.j2` extension by the pytest runner. E.g.
`ns1/named.conf.j2` will become `ns1/named.conf` during test setup. To
avoid automatic rendering, use `.j2.manual` extension and render the
files manually at test time.
New `templates` pytest fixture has been added. Its `render()` function
can be used to render a template with custom test variables. This can be
useful to fill in different config options during the test. With
advanced jinja2 template syntax, it can also be used to include/omit
entire sections of the config file rather than using `named1.conf.in`,
`named2.conf.in` etc.
Unify the different loggers (conftest, module, test) into a single
interface. Remove the need to select the proper logger by automatically
selecting the most-specific logger currently available.
This also removes the need to use the logger/mlogger fixtures manually
and pass these around. This was especially annoying and unwieldy when
splitting the test cases into functions, because logger had to always be
passed around. Instead, it is now possible to use the
isctest.log.(debug,info,warning,error) functions.
Rewrite and reorganize the test documentation to focus on the pytest
runner, omit any mentions of the legacy runner which are no longer
relevant, and mention a few pytest tricks.
