[tests] Update to use lit_config and lit package, as appropriate.

git-svn-id: https://llvm.org/svn/llvm-project/lnt/trunk@188098 91177308-0d34-0410-b5e6-96231b3b80d8
[app] Factor out App.create_with_instance().

git-svn-id: https://llvm.org/svn/llvm-project/lnt/trunk@188099 91177308-0d34-0410-b5e6-96231b3b80d8
[lnttool] Add a view-comparison command, for quickly viewing results.

 - This command acts as a viewer for two raw report files, by spinning up a new
   temporary LNT instance, importing the data, then opening a webbrowser to view
   the result.

git-svn-id: https://llvm.org/svn/llvm-project/lnt/trunk@188100 91177308-0d34-0410-b5e6-96231b3b80d8