MB-100 fix crash in ns_log caused by ns_config_ets_dup and

ns_node_disco being called before they are properly started

here are the callstacks that cause the crash:

ns_log:do_log
cluster_compat_mode:split_live_nodes_by_version
cluster_compat_mode:is_node_compatible
cluster_compat_mode:get_compat_version
ns_config_ets_dup:unreliable_read_key

ns_log:do_log
cluster_compat_mode:split_live_nodes_by_version
ns_node_disco:nodes_actual_proper

Change-Id: I22b3f484338f8ee0c1ed51e0c414cb29cd8eb869
Reviewed-on: http://review.couchbase.org/29909
Tested-by: Artem Stemkovski <artem@couchbase.com>
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>