Add ccache collection support to tools

Add ccache collection support to tools

* "kdestroy -A" destroys all caches in collection.
* "kinit princ" searches the collection for a matching cache and
  overwrites it, or creates a new cache in the collection, if the
  type of the default cache is collection-enabled.  The chosen cache
  also becomes the primary cache for the collection.
* "klist -l" lists (in summary form) the caches in the collection.
* "klist -A" lists the content of all of the caches in the collection.
* "kswitch -c cache" (new command) makes cache the primary cache.
* "kswitch -p princ" makes the cache for princ the primary cache.

ticket: 6956

git-svn-id: svn://anonsvn.mit.edu/krb5/trunk@25157 dc483132-0cff-0310-8789-dd5450dbe970