tools-utils: Fix looking for vmlinux binary in debuginfo package

tools-utils: Fix looking for vmlinux binary in debuginfo package

When abipkgdiff is invoked on a `kernel' package,
compare_prepared_linux_kernel_packages fails to look for the `vmlinux'
file from the debuginfo package, because of a thinko.

Then, build_corpus_group_from_kernel_dist_under, also fails to find
`vmlinux' from the debuginfo package because of another thinko.

This patch fixes the two thinkos.

	* src/abg-tools-utils.cc
	(get_binary_paths_from_kernel_dist): Fix a thinko and really use
	the kernel_modules_root variable.  Look for modules under
	kernel_modules_root and look for vmlinux (if necessary) under
	debug_info_root. Add comments.
	(compare_prepared_linux_kernel_packages): Fix another thinko.  Now
	we do have the path to vmlinux, from debuginfo packages before
	getting into get_binary_paths_from_kernel_dist.

Signed-off-by: Guillermo E. Martinez <guillermo.e.martinez@oracle.com>
Signed-off-by: Dodji Seketeli <dodji@redhat.com>