[krbdev.mit.edu #8163] python test issues

[John Devitofranceschi via RT]

This seems trivial but...

The shebang line for the following files in src/tests is not the first line in the file. This breaks the tests when
trying to run them individually.

t_ccache.py
t_renprinc.py
t_stringattr.py

Also, most of the .py files are not executable and they probably should be.

This is useful when trying to run the scripts individually (in verbose mode) w/out having to explicitly running them using 'python' on the command line.

jd