Add CAStore for selfsigned certificates, force version to SSLv3

Redmine fails connecting to ldaps:// with our certain ldap server:
SSL3_GET_RECORD:decryption failed or bad record mac

CAStore and SSLv3 have to be setup for connection.
Verified by
openssl s_client -connect ldapserver.example.com:636 -CAfile /etc/openldap/certs/ca.cer -no_tls1_1
these commandline option were added to ldap.rb