Add support for k5srvutil -e keysalts

k5srvutil is a little more convenient to use for rolling keys than
kadmin is.  When migrating off 1DES, though, it may be desirable to
explicitly specify the desired keysalts.  This adds an option, -e, to
k5srvutil to specify desired keysalts.

[ghudson@mit.edu: style fix; make whitespace in keysalt list work]

ticket: 7589 (new)