certificate: actually print openssl errors

certificate: actually print openssl errors

print_errs (which is also called internally by die_now) will only
'warn' the collected error stack if the log level is set to tracing.
otherwise, it will just return the error message(s) corresponding to
the error stack as string.

while they are not always the most user-friendly ones, they do
provide additional context that might help to find out what is
actually causing a particular failure. both helpers here actually
provide a meaninful user friendly context (via $msg) as final line.

Signed-off-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>
 [ T: resolve merge conflict due to dropped warn helper ]
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>