In some cases, the numeric identifier doesn't correspond to the
directory name (i.e. `resolver` server in `shutdown` test, which is
supposed to be 10.53.0.3). These are typically servers that shouldn't be
auto-started by the runner, thus avoiding the typical `*ns<X>` name.
Support these server by allowing a fallback initialization with custom
numeric identifier in case it can't be parsed from the directory name.
Previously, these functions have been provided as fixtures. This was
limiting re-use, because it wasn't possible to call these outside of
tests / other fixtures without passing these utility functions around.
Move them into isctest.run package instead.
Enforcing pylint standards and default for our test code seems
counter-productive. Since most of the newly added code are tests or is
test-related, encountering these checks rarely make us refactor the code
in other ways and we just disable these checks individually. Code that
is too complex or convoluted will be pointed out in reviews anyways.
