Add a selenium test
tbb-testsuite: allow testing more than one bundle
Add options to disable mozmill or selenium tests
Get infos about bundle (os, version, language) from filename
If filename is a URL, download it
add support for sha256sums.txt tests

If we are given a sha256sums.txt file as argument, then we test all the
bundles compatible with current platform listed in the sha256sums.txt.
If sha256sums.txt file is a URL, then we download it and the bundle
files that are listed in it, and check their sha256sum.