Add OpenBSD default CA certificates file location

GitHub pull: https://github.com/OfflineIMAP/offlineimap/pull/120
Signed-off-by: Eygene Ryabinkin <rea@codelabs.ru>

Changelog.rst

@@ -8,6 +8,9 @@ ChangeLog
 OfflineIMAP v6.5.6.1 (YYYY-MM-DD)
 =================================
 
+* Added default CA bundle location for OpenBSD
+  (GitHub pull #120).
+
 * Added OpenSSL exception clause to our main GPL to allow
   people to link with OpenSSL in run-time.  It is needed
   at least for Debian, see

offlineimap/utils/distro.py

@@ -13,7 +13,7 @@ import os
 # one that corresponds to the existing file.
 __DEF_OS_LOCATIONS = {
     'freebsd': '/usr/local/share/certs/ca-root-nss.crt',
-    'openbsd': None,
+    'openbsd': '/etc/ssl/cert.pem',
     'netbsd': None,
     'dragonfly': None,
     'darwin': [