crypto: always reload tls-auth/crypt key contexts

crypto: always reload tls-auth/crypt key contexts

In preparation to having tls-auth/crypt keys per connection
block, it is important to ensure that such material is always
reloaded upon SIGUSR1, no matter if `persist-key` was specified
or not.

This is required because when moving from one remote to the
other the key may change and thus the key context needs to
be refreshed.

To ensure that the `persist-key` logic will still work
as expected, the tls-auth/crypt key is pre-loaded so that
the keyfile is not required at runtime.

Trac: #720
Cc: Steffan Karger <steffan@karger.me>
Signed-off-by: Antonio Quartulli <a@unstable.cc>
Acked-by: Steffan Karger <steffan.karger@fox-it.com>
Message-Id: <20180708024517.27108-1-a@unstable.cc>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg17237.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>