scripts: test for imported ELFFile instead of setting it to None

mypy fails with:
Incompatible types in assignment
        (expression has type "None", variable has type "Type[ELFFile]")

this happens because of the code:
    try:
        from elftools.elf.elffile import ELFFile
    except ImportError:
        ELFFile = None

ELFFile is set to None to allow later code to check if ELFFile was
imported by checking against None. Instead of setting ELFFile to None,
then update testing code to check if the class has been loaded, as:
    if globals().get('ELFFile') is None:

Update the try-catch to `pass`.

Removed ELFFile cargo cult from intel_cyclonev.py and fix pylint
warnings.

Disable duplicate code check. The intel_cyclonev.py is already based
upon openocd.py, so although the duplication detection is correct then
this should not prevent other code changes / fixes to those files from
being applied.

Signed-off-by: Torsten Rasmussen <Torsten.Rasmussen@nordicsemi.no>