crypto: load all certificates in X509 CA file

crypto: load all certificates in X509 CA file

Some CA files may contain multiple intermediaries and roots of trust.
These may not fit into the hard-coded limit of 16.

Extend the validation code to allocate enough space to load all of the
certificates present in the CA file and ensure they are cleaned up.

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Henry Kleynhans <hkleynhans@fb.com>
[DB: drop MAX_CERTS constant & whitespace tweaks]
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>