Only run MarkInstall() on pkgs with a InstallVer in pkgDistUpgrade

This prevents MarkInstall() from having side-effects like in
LP: #1304403 where MarkInstall() on a non-upradable
packages causes a MarkKeep() which in turn creates havoc
test/integration/test-bug-591882-conkeror: remove previously failing test as this is no longer a failure condition that can be triggered