Improved (or warned about lack of) error handling.

It would be safer for dumpstate to exit when execvp on a child fails; a
common occurrence is when a list of command arguments is missing NULL.

dumpstate should be more robust to detect those missing NULL-terminated
args, but that will be addressed in a future change.

BUG: 27804637
BUG: 27832567
Change-Id: Ibcbe46041a86b16e365fbb40613b8c4bdf39744c