remove dependency on libkadm5clnt_mit.so

[iNecas]

The libkadm5clnt_mit.so is considered highly unstable by the upstream and it's quite likely it gets removed form/broken in next krb5 releases (see https://bugzilla.redhat.com/show_bug.cgi?id=1330431 for more details).

[djberg96]

@iNecas What's the current standard? Heimdal?

[pkis]

While the kerberos protocol is standardized (RFC 4120) the admin protocol is not.

Regarding the API, admin.h states:
/*

• This API is not considered as stable as the main krb5 API.
  *
• - We may make arbitrary incompatible changes between feature
• releases (e.g. from 1.7 to 1.8).
• - We will make some effort to avoid making incompatible changes for
• bugfix releases, but will make them if necessary.
  */

Not sure about Heimdal, but I have not found any reference to admin API.

[sonOfRa]

I'm not sure how I can work around this. While redhat doesn't seem to use the kadmin API functionality of this gem, I use it quite extensively myself, so removing it would be counterproductive, as we don't have anything else that provides the same API (short of dropping shell commands and piping output into them). I'm not sure how to resolve this as of now, so I'd say the dependency will stay for now, unless someone comes up with a good idea to work around it.

[djberg96]

Although I resisted it originally, I now think the admin portion should be split into its own gem. While this doesn't wholly address the issue here, it would at least allow the client portion to ignore such issues.