This fixes a problem which appeared after bossac version was downgraded
to 1.7 which no longer accepts the -o/--offset parameter. Now the offset
is fed to bossac executable only if it's explicitly provided and not by
default.
Signed-off-by: Kuba Sanak <contact@kuba.fyi>
Add self.require() checks before running commands. Increase test
coverage, including for this feature, while we are here.
Signed-off-by: Marti Bolivar <marti.bolivar@nordicsemi.no>