Always use an in-process webserver, removing the need for apache - and
hopefuly providing better accuracy for numbers.
This means that we know have to copy the pagesets in the talos dir on
harness.
On windows, some pagesets paths were too long due to that, so the
solution is to replace "page_load_test" with "tests".
This removes ambiguity as to which modules are being imported, making
import slightly faster as Python doesn't need to test so many
directories for file presence.
All files should already be using absolute imports because mach command
modules aren't imported to the package they belong to: they instead
belong to the "mach" package. So relative imports shouldn't have been
used.
