Handle corrupt cert.pem or ca.pem files correctly
Code review markups - check file existence and handle a mismatched private/public keypair
Check issuing CA name against ca.pem certificate
Core review feedback - make ca.pem checking independent of cert.pem checking
Merge pull request #78 from Metaswitch/missing_cert_fix

[Reviewer: Matt] Handle corrupt cert.pem or ca.pem files correctly