Fix tls_connection shutdown cleanup

The SSL library maintains an internal table of CA certificates
(ssl_otp_cacertificate_db). This is supposed to be cleaned up when the
last connection using a certificate closes, however there's two problems
in R16B02 (and in the current master branch on github):

* When CA certificates are provided as binary blobs, rather than by
filename (ie, #ssl_options.cacerts is set, but #ssl_options.cacertfile
is undefined) the cleanup never occurs due to an incorrect pattern
match in tls_connection:handle_trusted_certs_db/1. This causes the
table to grow unchecked because each connection adds a new entry.

* When the process exits abnormally, tls_connection:terminate/1 is never
called because the trap_exit process flag is not set and so similarly
the table (and everything else cleaned in terminate/1, for that
matter) is not cleaned up. This doesn't affect "normal" termination
caused by the connection closing because terminate/1 is called
explicitly from handle_sync_event/4, rather that relying on gen_fsm's
automatic calling.