Faults found by PropEr

[WoelkiM]

Poblems which have been recognized in Proper are
in node_watcher_qc and riak_core_claim_statem ( method claim ).

• node_watcher_qc
• riak_core_claim_statem

For execution, lines 41 - 45 in node_watcher_qc must be uncomment and can then be executed with "./rebar3 as proper do eunit -m node_watcher_qc".
Skrink node_watcher_qc:
https://travis-ci.org/github/riak-core-lite/riak_core_lite/jobs/696417379#L713

Uncomment lines 53 and 54; execution with "./rebar3 as proper do eunit -m riak_core_claim_statem".
Skrink claim_statem:

shrink_riak_core_claim_statem.txt