KrbOfferedEncryptionTypes setting isn't always respected

[smashery]

The KrbOfferedEncryptionTypes setting isn't respected if there's already a "matching" ticket in the kerberos cache.

Steps to reproduce

• Setup: clear the kerberos cache (klist -d)
• Use a kerberos-supported module
• Run the module with kerberos auth (should default to AES256)
• Observe the communications in wireshark - will likely be AES256
• Note that the kerberos cache now has tickets (klist)
• Re-run the module, forcibly setting krbofferedencryptiontypes to RC4-HMAC
• Observe the communications in wireshark - should be RC4-HMAC, but is actually AES256
• Delete kerberos tickets: klist -d
• Re-run the module, forcibly setting krbofferedencryptiontypes to RC4-HMAC
• Observe the communications in wireshark - is now RC4-HMAC

Expected behaviour

• If an encryption type is set that does not match tickets in the kerberos cache, it should re-request a Kerberos ticket OR warn the user about this edge case

Tested on metasploit commit: c9dfb7e

[Neustradamus]

To follow :)