Add --base option to test-perf.
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Add a `--base <URL>` option to test-perf, which is handy for two reasons: a) it reduces randomness in tests by allowing tests to be file URLs, and b) it doesn't require running the test suite as root (the tp5n manifest hardwires tests served from port 80 on localhost).
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in testing_commands.py, I linked the new command to test_perf.sh
in test_perf.sh, it would prepare tp5n.zip and virtual environment
then run test_all.sh
