tools/qa-checks: Refactor shell check script as a checker module

This patch adapts the standalone shellcheck script, aligning it with the other
modular checks. The depreciated code-check and virtual environment wrapper
within meta-ewaol-config is also removed in preference for the more generic
run-checks.py script and ModulesVirtualEnv class.

Issue-Id: SCM-2584
Issue-Id: SCM-2585
Signed-off-by: Richard Neill <richard.neill@arm.com>
Change-Id: Iea9855a17eba3d80f09954a568f216280d273e3d