When we failed to load pkcs12 cert print warning

Print actual error when we failed to load pkcs12 cert and
falling back to the default implemntation, as exception may
not be related to certificate or its format like an issue
with wrong methods during cryptography version mismatch

*** AttributeError: module 'OpenSSL.crypto' has no attribute 'load_pkcs12'

Related-Prod: PRODX-39931
Change-Id: I85c8a615c4f2e08e28939805ae0e9b2028dadaed

Author: jumpojoy

octavia/certificates/manager/barbican.py

@@ -120,7 +120,10 @@ def get_cert(self, context, cert_ref, resource_ref=None, check_only=False,
             return pkcs12.PKCS12Cert(cert_secret.payload)
         except exceptions.UnreadablePKCS12:
             raise
-        except Exception:
+        except Exception as e:
+            LOG.warning('Failed to load PKCS12Cert for secret %s with %s',
+                        cert_ref, str(e))
+            LOG.warning('Falling back to the barbican_legacy implementation.')
             # If our get fails, try with the legacy driver.
             # TODO(rm_work): Remove this code when the deprecation cycle for
             # the legacy driver is complete.