Piglit's HTML generator dies if you have multiple piglit instances
I thought this was a mako bug but, no, it's a piglit bug:
https://github.com/sqlalchemy/mako/issues/308
The problem is that we have a _TEMP_DIR
which isn't sufficiently unique to the specific piglit instance. The result is that if you have two piglit instances and try to use the HTML summary from both of them, you'll end up with stale mako templates in one and piglit will crash in bizarre ways.