OSDP CP init should make sure that the SCBKs are different and non-zero.

[sidcha]

Now the application can setup a CP with different SCBKs for each PD without passing a master key. But an ignorant programmer can pass the same SCBK buffer to all the PDs or worse, pass all zeros.

LibOSDP should do some preliminary checks on SCBK we receive from the user.

This issue was revealed from PR: #56