security/openvpn: bugfix update to 2.5.5

Bugfixes (FreeBSD-specific):

• improve "make check" to notice if "openvpn --show-cipher" crashes
• improve argv unit tests
• ensure unit tests work with mbedTLS builds without BF-CBC ciphers
• include "--push-remove" in the output of "openvpn --help"
• fix "resolvconf -p" invocation in example "up" script
• fix "common_name" environment for script calls when "--username-as-common-name" is in effect (Trac #1434)

Documentation:

• move "push-peer-info" documentation from "server options" to "client" (where it belongs)
• correct "foreign_option_{n}" typo in manpage
• update IRC information in CONTRIBUTING.rst (libera.chat)
• README.down-root: fix plugin module name