Enable json export of graph data

If passing json=true to the graphing page, export the graph data as json instead of HTML.

git-svn-id: https://llvm.org/svn/llvm-project/lnt/trunk@204366 91177308-0d34-0410-b5e6-96231b3b80d8
Add some simple logging to files

To help diagnose server failures more easily.

git-svn-id: https://llvm.org/svn/llvm-project/lnt/trunk@204367 91177308-0d34-0410-b5e6-96231b3b80d8