crash-reporter: Use chromeos::KeyValueStore.

Make the crash reporter use libchromeos's KeyValueStore
class to read its log-collection config file and
/etc/lsb-release instead of its own parsing code.

Also update the log-collection config file to split long
commands across multiple lines and to use '=' instead of ':'
to separate executable names from commands.

BUG=chromium:452520
TEST=updated tests; also triggered powerd and chrome crashes
     and checked that logs were attached

Change-Id: I4e2447712869608f32a4ae38f5d5cb9c6046af14
Reviewed-on: https://chromium-review.googlesource.com/244121


Reviewed-by: Dan Erat <derat@chromium.org>
Commit-Queue: Dan Erat <derat@chromium.org>
Tested-by: Dan Erat <derat@chromium.org>