security/krb5*: Allow the user to specify state directory locations

localstatedir and runstatedir are set to ${PREFIX}/var and
${PREFIX}/var/run respectively. Users who wish to put their KDC
DB elsewhere can set the following in make.conf:
KRB5_LOCALSTATEDIR=/va
KRB5_RUNSTATEDIR=/var/run.

Unfortunately defaulting to /var instead of the current default would
result in MIT KDC not finding its KDC DB files. This would be disruptive
to all MIT KDC users. But new users of MIT KRB5 KDC can set the pathname
above as desired.

PR: 267560