Don't hard fail when we couldn't find an entry point for an extension

Don't hard fail when we couldn't find an entry point for an extension

It doesn't make a ton of sense, it's just pointing out that we have
a weird extension for which we cannot detect a standard entry point
for. These (unfortunately) exist, but they're easily worked around
using --list-file

Removing the hard failure allows you to use the two options in
tandem... --extension-dir for the initial pass and then --list-file
for the weirdo outstanding ones

Change-Id: I3d9cf1d614dacaa91fb2092019ccf1d14d61ccab