scripts: Suppress/fix undefined variable pylint warnings

dtlib.py and guiconfig.py do some hackery to build token and image
variable names, which triggers spurious pylint warnings like

    scripts/dts/dtlib.py:243:28: E0602: Undefined variable '_T_LABEL'
    (undefined-variable)

Suppress the warning for those files. The generated names get used in
lots of places.

Also suppress some warnings in doc/conf.py ('tags' is from Sphinx), and
fix a legitimate issue in scripts/dts/testdtlib.py.

This pylint check is useful enough to want enabled in the upcoming CI
check.

Signed-off-by: Ulf Magnusson <Ulf.Magnusson@nordicsemi.no>
4 files changed