PixelReplaceStep returns strange output filenames from save_results=True

[stscijgbot-jp]

Issue JP-3784 was created on JIRA by Ned Molter:

Running the PixelReplaceStep using regression test data from nirspec/ifu as follows:

fn = glob.glob(stem + "jw01249*_cal.fits")
container = datamodels.ModelContainer(fn)
PixelReplaceStep.call(container, save_results=True, skip=False)

returns filenames that look like "step_PixelReplaceStep_3_pixelreplacestep.fits".  The output filenames should be updated to be more descriptive and more closely match other steps.  Each input model in the list is still saved separately according to an index, so setting this fix as low priority.