Exclude statefs from an output of /bin/df

In the case when statefs crashes, df may hang indefinitely while trying
to access the directory where it is mounted. Statefs wasn't even
included in the output so we're not losing any information.
Check that statefs haven't crashed before accessing it

Dumper script may hang on access to /run/state.
Merge pull request #57 from xhaakon/master

Check that statefs haven't crashed before accessing it