Support third-party modules that use CamelCase

Add logic to third-party 'module' support to also work with external
packages that use CamelCase for their package "standard" variables (i.e.
<name>_{FOUND,LIBRARIES,INCLUDE_DIRS}). In particular, ParaView requires
this to use external QtTesting.

Change-Id: I645d2374ec2503eac7d226ef948f6f4b01f8de01
Merge topic 'fix-find-external-3p' into master

a982cf46 Support third-party modules that use CamelCase