generic improvements for the testsbed

* fix run-tests so it can return != 0
* bail out if prepare fails
* add more sanity checks to prepare
* generalize usb-ids, paths
* add test for flashing from application mode
* add test reading simcards via pysim

Change-Id: I246224e29e5936b4fe40cf7d7a5ff83c9940d121
20 files changed