util: Rework some checks in the m5 util scons to use Configure().

util: Rework some checks in the m5 util scons to use Configure().

This is the official scons way to check for things on the system. This
adds two custom checks, one for java packages and one for pkg-config
packages. This change also adds a check for the org.junit java package
which is/will be used for a test for the java wrapper.

Change-Id: I59ca559f257a4c671e9b72a50b5635b5eb61ee69
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/28180
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Bobby R. Bruce <bbruce@ucdavis.edu>
Maintainer: Gabe Black <gabe.black@gmail.com>