Bugfix: Fix AFSecurityPolicyTests

Unit Tests were failing to compile.   It appears that the pinning mode is construction-injectected, and the unit tests were using the setter.   

Also, testPolicyWithPinningModeIsSetToValidatesDomainName was failing.  It was expecting validatesDomainName to be YES for AFSSLPinningModeNone, which didn't make sense conceptually and the code said it should be NO, so I changed it.   This should  be double checked, as I've never used the SSL Pinning API.