Add test to "test_all.sh" to run all pytests

Requested Update

Description

• Add a call to test_all.sh to run all pytests

Background and Motivation

• Formalize the process of calling units tests in all repos.
• May want to wait until we formalize the testing process (ie, potentially not having to clone geoips repo locally in order to run any tests - now since "check_code.sh" is called from $GEOIPS_PACKAGES_DIR, geoips must be cloned to run any plugin repo tests.
• Something like "if -e tests/test_pytest; then pytest tests/test_pytest

Alternative Solutions

• [ OPTIONAL: If appropriate, list alternative fixes that could be considered]

Environment

• [ IF APPROPRIATE: Corresponding repository versions ]

Code to demonstrate issue

• [ IF APPROPRIATE: Can include steps here to identify/demonstrate bug fix or desired feature ]

Checklist for Completion

• <!--- Include a list of steps that must be complete in order to close this Issue --->

Open test_all.sh and inspect how existing checks are invoked, then review the proposed tests/test_pytest path and the role of check_code.sh from GEOIPS_PACKAGES_DIR. Done means test_all.sh invokes the repository's pytest tests in the agreed testing workflow; the issue notes that this process may still change.