Always define the path DNSSEC_OPENSSL_CONF
The variable was None by default and set to /etc/ipa/dnssec/openssl.cnf
for fedora only because the code is specific to the support of pkcs11
engine for bind. As a consequence ipa-backup had a "None" value in the
list of files to backup and failed on Exception.
ipa-backup code is able to handle missing files, and the code using
the pkcs11 engine is called only when NAMED_OPENSSL_ENGINE is set
(only in fedora so far). It is safe to always define a value for
DNSSEC_OPENSSL_CONF even on os where it does not exist.
The fix also improves the method used to verify that a path exists.
Reviewed-By: Alexander Bokovoy <email@example.com>