Tools: Install ksh

Monitoring the access times of /bin/ksh shows reads:

a) from time to time cluster-wide simultaneously, probably by a Puppet
   change,

b) on individual hosts, mostly tools-login and tools-dev, at different
   times.

So apparently ksh is used consciously by someone or something.

Change-Id: I467ed522d6919963524cccf42c78d0ed3fcfe38b