Let people who run the nightly tester specify paths to external tests, instead

Let people who run the nightly tester specify paths to external tests, instead
of having to hack the nightly tester script itself.

as an example, I use the following for my machine:

$HOME/llvm/utils/NightlyTest.pl -parallel -release -enable-llcbeta \
     -spec2000path /Volumes/ProjectsDisk/cvs/benchmarks/speccpu2000-llvm/benchspec/ \
     -povraypath /Volumes/ProjectsDisk/cvs/benchmarks/povray31 \
     -namdpath /Volumes/ProjectsDisk/cvs/benchmarks/namd

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@24136 91177308-0d34-0410-b5e6-96231b3b80d8