ACCUMULO-3445 ACCUMULO-3446 Throw an RTE on keytab login failure

Also relocates this class into "server code" as it makes
no sense to be located in the client package. Clients will
just need an active ticket, it's of no concern to us how they
get that ticket.
Merge branch '1.5' into 1.6
ACCUMULO-3446 Git didn't automatically rename it.

server/src changed to server/base/src from 1.5 to 1.6.