--component does not work with --preserve

[matthiaskrgr]

1. run CBR with --preserve and do a bisection.
2. now do the same bisection but with --component rls for example
   => cbr will NOT notice that it lacks the component rls for the toolchains it has already installed!

I have the feeling that we just check "is the nightly there? yes? then let's go!" instead of actually checking if the specified components are installed and then installing the missing components as needed.

When I run it without --preserve (but with -c) it will eventually notice "hey I could not download that component" :|