test/py: Make print statements python 3.x safe

In python 3.x print must be called as a function rather than used as a
statement. Update uses of print to the function call syntax in order to
be python 3.x safe.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Reviewed-by: Stephen Warren <swarren@nvidia.com>

test/py/u_boot_spawn.py

@@ -58,7 +58,7 @@ class Spawn(object):
                     os.chdir(cwd)
                 os.execvp(args[0], args)
             except:
-                print 'CHILD EXECEPTION:'
+                print('CHILD EXECEPTION:')
                 import traceback
                 traceback.print_exc()
             finally: