Allow isprintable() util function to work with unicode

Fixes #6842

lib/ansible/utils/string_functions.py

@@ -1,9 +1,12 @@
 def isprintable(instring):
+    if isinstance(instring, str):
         #http://stackoverflow.com/a/3637294
         import string
         printset = set(string.printable)
         isprintable = set(instring).issubset(printset)
         return isprintable
+    else:
+        return True
 
 def count_newlines_from_end(str):
     i = len(str)