Control plane load balancing

[olix0r]

commit 6057920256be10d5a55aef38424d0c224dd033b1 (HEAD -> ver/dns-srv, origin/ver/dns-srv)
Merge: b3808cc5 bff503e7
Author: Oliver Gould <ver@buoyant.io>
Date:   Tue Aug 25 01:29:59 2020 +0000

    Merge branch 'ver/dns-fg' into ver/dns-srv
    
    This merge removes some try_stream! uses to satisfy `Unpin`
    requirements.

commit bff503e74b5ea4798a81fc343ea649cd84e19397 (origin/ver/dns-fg, ver/dns-fg)
Author: Oliver Gould <ver@buoyant.io>
Date:   Tue Aug 25 00:17:24 2020 +0000

    dns: Run DNS resolutions on the main runtime
    
    DNS resolutions are run on the admin runtime. This requires an
    unnecessary layer of indirection around the resolver, including an MPSC.
    
    Now that we allow the main runtime to use more than one thread, it's
    preferable to do this discovery on the main runtime and we can simplify
    the implementation.

commit b3808cc55b4f5f8e2d6209661a203dee75744d2f
Author: Oliver Gould <ver@buoyant.io>
Date:   Tue Aug 25 00:04:29 2020 +0000

    lookup_service_ips => lookup_service_addrs

commit 2f3e7c43c6f0a0f31640535aa2e684d4c62d528e
Author: Oliver Gould <ver@buoyant.io>
Date:   Mon Aug 24 23:59:09 2020 +0000

    undo unnecessarty change

commit 9154fcdc60d9679f6187f7eb500856ca75edd7a3
Author: Oliver Gould <ver@buoyant.io>
Date:   Mon Aug 24 23:49:59 2020 +0000

    Use map_endpoint to build control client targets

commit 16d5014ef3ff0b901b81e2854e1a1d57648b1c5c
Author: Oliver Gould <ver@buoyant.io>
Date:   Mon Aug 24 23:03:57 2020 +0000

    undo errant change

commit 7c9e529fc18c56468dc20a308d70c327db411ca3
Author: Oliver Gould <ver@buoyant.io>
Date:   Mon Aug 24 23:01:39 2020 +0000

    dns-resolve: Always use resets
    
    There's no reason that we have to maintain the resolution state now that
    we have a Reset type.
    
    Furthermore, we can use a unit endpoint type, since it is ignored.

[olix0r]

Incorporates #637

[zaharidichev]

LGTM. There are still conflicts however