modules: Do not hide errors using IPA *_show command with Exception

When searching for objects with *_show IPA API command, most plugins
were hiding errors other than "ipalib_errors.NotFound" by handling the
broad exception Exception instead.

This patch uses "ipalib_errors.NotFound" whenever "*_show" is used so
that the only exception handled is when an object is not found. Other
errors will not be handled making the module break as expected.