Update directory to find performance graphs in for syncing to SF in nightly

I thought cronlogdir would be NightlyPerformance for performance and compiler
performance testing, but that's only true for performance testing. This
switches to use CHPL_TEST_PERF_DIR and CHPL_TEST_COMP_PERF_DIR which are
directly responsible for telling start_test where to put the graphs and html
directory.
Merge pull request #870 from ronawho/fix-perf-graph-sync

Update directory to find perf graphs in for syncing to SF in nightly

[reviewed by @thomasvandoren]

I thought cronlogdir would be NightlyPerformance for performance and compiler
performance testing, but that's only true for performance testing. This
switches to use CHPL_TEST_PERF_DIR and CHPL_TEST_COMP_PERF_DIR which are
directly responsible for telling start_test where to put the graphs and html
directory.