Bug 1092074 - Make LogShake feature resilient to read/parse errors. r=gwagner

In the event of broken/unexpected things, we would like to have even a
partial log set dump. This happens for parsing properties values on
Kitkat builds: the current code does all the parsing itself, but the
format of storage of properties evolved with Kitkat base system, and
this makes LogParser to fail, as documented in bug 1079322. Even if we
miss some values, it can still be useful to have the other remaining
ones.