MB-10466 Revert "Revert "MB-10953 Clear ssl PEM cache after saving certificates.""

This reverts commit 4d64f7e4dc749778d46149a24d77e8bb111c1528.

We seem to have switched to R16 so resurrecting this change. It also
fixes a deadlock with stopping ssl application in
ns_ssl_services_setup init function.

Change-Id: I9eea4ca617a3e7d061c47d9a953dddddb3a356ec
Reviewed-on: http://review.couchbase.org/38454
Tested-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Reviewed-by: Artem Stemkovski <artem@couchbase.com>