Changed Machine.DEFAULT_BASELINE_REVISION to be set from the lnt config
file with a default value that is the same as the old hardcoded
baseline. This is needed because we want LNT to be able to be used on
other code bases besides LLVM if needed.

git-svn-id: https://llvm.org/svn/llvm-project/lnt/trunk@176850 91177308-0d34-0410-b5e6-96231b3b80d8
Refactored Machine.get_baseline_run into two different methods,
Machine.get_closest_reported_order which returns the closest previous
order to a specific revision that the machine reported on and
Machine.get_baseline_run which invokes said method passing in
Machine.DEFAULT_BASELINE_REVISION.

git-svn-id: https://llvm.org/svn/llvm-project/lnt/trunk@176851 91177308-0d34-0410-b5e6-96231b3b80d8
Fixed typo.

git-svn-id: https://llvm.org/svn/llvm-project/lnt/trunk@176852 91177308-0d34-0410-b5e6-96231b3b80d8