Set the default certificate authority bundle to the embedded copy

SSL peer verification was failing on TLS servers with the error message:

SSL_connect returned=1 errno=0 state=SSLv3 read server certificate B: certificate verify failed

It appears that when using the mail gem, the default certificate store is not set in Ruby v2.1.6 or in the mailer code.

See: https://gitlab.com/gitlab-org/gitlab-ce/issues/1558