QA: Add a set of checks for bash-completion files

Add checks for common mistakes when installing bash completion files:
legacy directory, incorrect naming, missing aliases, deprecated 'have'
function.

Acked-by: Brian Dolbec <dolsen@gentoo.org>
Split install_qa_check() into install-qa-check.d scripts

Convert the horrendous install_qa_check() function into a plug-in system
that calls separate QA checking scripts from install-qa-check.d.
Merge branch 'master' into all-in-one
Merge branch 'install-qa-check-refactor' into all-in-one