Revert "MODCLUSTER-338 Advertize adds a message digest even if security key is not configured"

This reverts commit 2e3f92b67b0d708fbf2895eaffb75e8d555477f1.
[MODCLUSTER-337] Revisit: if security key is not used, verify using zero byte array
[MODCLUSTER-338] Fix tests to send properly formed advertise message packet
Merge pull request #58 from rhusar/MODCLUSTER-337/revisit

Revisit MODCLUSTER-337 & MODCLUSTER-338