Krb5 dep8 tests

Add some simple DEP8 tests to the krb5 package. I'm almost removing the simpler kinit one, because it's essentially part of the more complex slapd-gssapi one. But if kinit fails, it could be simpler to diagnose and analyse if it were its own simple test. Let me know what you prefer, and if there is another test you would like to see done here that is not too complex.

Here is the output of an autopkgtest run using a sid lxd container: https://people.ubuntu.com/~ahasenack/krb5-dep8-output-lxd/