Fixed gen_key to expect the proper PIV Key references.

This pull request is to bring key generation on piv-tool in line with what is documented in NIST 800-78-3 and in the man page.  Typically you won't want to generate Card Management keys unless you really know what you are doing.  Please comment if you think that the 0x9B keyId should be left in, and I will adjust accordingly.

### From the Commit
0x9B is defined as the Card Management Key, and probably shouldn't be
regenerated.  0x9E is the Card Authentication key which is what you
should be generating keys for.  This also brings piv-tool in line with
the documentation that states 0x9A, 0x9C, 0x9D and 0x9E are the proper
keyIds to use.