Clean up Dockerfiles

[ellismg]

• Delete the unversioned directories, CI and VSO has been updated to
  use the new names.
• Remove adding llvm.org/apt/ to the sources list. The LLVM team
  suspended this 05/31/2016 so building containers from scratch with
  these Dockerfiles was failing. It turns out that lldb-3.6 (which is
  what we were using the source for) is now in Ubuntu 14.04 (trusty) so
  we didn't need it anymore. LLDB is only required there because
  CoreCLR has a dependency on it for some debugging stuff, and we need
  it on the box so the depends sniffing when doing the deb package
  builds gets confused if the imports are un-resolved. When we go to
  add packages for debian.8, we'll need to come up with a stragegy to
  get this package or turn off the auto-sniffing.
• I also shrunk down the list of packages to install based on a humna's
  understanding of the dependencies of CoreCLR and CoreFX instead of
  what a complication ldd invocation piped across dpkg searching told
  us. This is much more readable and a better indication of the CLR
  dependencies, IMHO

[dnfclas]

Hi @ellismg, I'm your friendly neighborhood .NET Foundation Pull Request Bot (You can call me DNFBOT). Thanks for your contribution!
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[ellismg]

@brthor @MichaelSimons My docker-fu is pretty weak, so maybe you want to take a look. I'm specifically interested in if the apt-get clean && rm -rf /var/apt/lists/* is a best practice or not in each layer (the guidance I found was mixed). I found that with and without it I was getting periodic hash mismatch errors, doing the cache busting in each layer seemed safer, but again I'm not an expert.

This should address the invalid GPG key errors we were seeing (I expect the will happen more and more often as CI machines are recycled and the prebuilt images are no longer in caches).

[ellismg]

Should CI be triggered on this branch now? Should I push this into master first instead?

[brthor]

I'm not sure why CI isn't running here. I will look into this, this morning.

[brthor]

After this goes in
dotnet/dotnet-ci#301

We should have CI for this.

[dnfclas]

Hi @ellismg, I'm your friendly neighborhood .NET Foundation Pull Request Bot (You can call me DNFBOT). Thanks for your contribution!
You've already signed the contribution license agreement. Thanks!

The agreement was validated by .NET Foundation and real humans are currently evaluating your PR.

TTYL, DNFBOT;

[brthor]

@mmitche Any ideas why the permissions on this directory might be messed up in CI?

11:45:32 error: Access to the path '/Users/dotnet-bot/.nuget/packages/' is denied.

This is on dci-macpro-02

[mmitche]

@ellismg Ahh cool thanks for the heads up. It was created as root

[brthor]

@dotnet-bot test OSX x64 Release Build please

[eerhardt]

Is this mergable? So we can unblock Jenkins?

[ellismg]

I'll merge this now to unblock CI and address feedback in a follow up later today/tonight.