Support all install-qa-check.d locations and overrides

Update the install-qa-check.d handling code to conform to GLEP 65.
Collect files from all defined locations, order them lexically by name
and run each uniquely named script once. Make scripts in higher priority
locations override lower priority locations properly.
Fix TypeError when using `emerge -C` without package name.
ebuild.sh: fix pkg_setup env for binary packages (528274)

In commit 743b3337644fbb3ea461d3a9137c9ac85e163f03, support for binary
packages broke, since binary packages must load the environment from
$T/environment. This patch fixes the logic to handle binary packages
correctly.

Fixes: 743b3337644f ("ebuild.sh: force fresh env for pkg_setup (528274)")
X-Gentoo-Bug: 528274
X-Gentoo-Bug-URL: https://bugs.gentoo.org/show_bug.cgi?id=528274
Acked-by: Brian Dolbec <dolsen@gentoo.org>