qa/admin/check-manifest: extend to check that packages are really available
qa/admin/check-manifest: extend to check that packages are really available

Check all packages from manifest after skip and unavailable have
been removed to make sure they really are available.

Add fast-path cacheing of available packages ... only for apt/dpkg so
far, others will come later.

adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp