Bugs in find_package_local

[nlslatt]

Describe the bug
When find_package_local fails to find the package, the list of search paths that it prints is incorrect. The printing logic assumes that the ${pkg_name}_DIR variable was unchanged during the loop over potential subdirectories containing the needed cmake files, which is incorrect. Additionally, the subdirectory existence check includes an undefined variable, pkg_prefix.

To Reproduce
Steps to reproduce the behavior:

1. Example/test/snippet of code that fails
2. Compiler, platform, libraries
3. Run command: number of processors, threading options, etc.
4. See error

Expected behavior
A clear and concise description of what you expected to happen.

Screenshots
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Platform (please complete the following information):

• Supercomputer or desktop [e.g., Trinity, Sierra)
• Compiler environment [e.g., clang-3.9, gcc8]
• Libraries [e.g., mpich-2, openmpi)
• Commit ID or release of VT [e.g., vt-1.0.0]

Additional context
Add any other context about the problem here.

[nlslatt]

The same problem exists in checkpoint (see DARMA-tasking/magistrate#163).