Since 11c14bd2f5 CA certificates referenced in ca sections were
enumerated by two credential sets if they were also stored in
ipsec.d/cacerts. This caused duplicate certificate requests to
get sent. All CA certificates, whether loaded automatically or
via a ca section, are now stored in stroke_ca_t.
Certificates referenced in ca sections are now also reloaded
when `ipsec rereadcacerts` is used.
This makes these CA certificates independent from the purge issued by reread
commands. Certificates loaded by CA sections can be removed through ipsec.conf
update/reread, while CA certificates loaded implicitly from ipsec.d/cacerts
can individually be reread using ipsec rereadcacerts.