Use kadmin script mode in Python tests

Use kadmin script mode in Python tests

In k5test, rename kadmin_local to kadminl and remove the run_kadminl()
K5Realm method.  Update all scripts to use realm.run([kadminl, 'cmd',
...]).  run_kadmin() still exists but takes an argument array instead
of a query string.

Where we touch test code, rename "output" to "out" (since "output" is
a function name exported by k5test.py), elide ":normal" from salt
strings, and use expressions like realm.krbtgt_princ instead of
manually composed principal names where appropriate.  In
t_kadmin_acl.py, get rid of the delprinc() helper since the equivalent
is now concise enough to be written out each time.  In t_policy.py,
remove some inoperative getprinc invocations and reorder some tests
which didn't correspond to their comment headers.