scripts: Simplify code with sys.exit(<string>)

Promote a handy and often-overlooked sys.exit() feature: Passing it a
string (or any other non-int object) prints it to stderr and exits with
status 1.

See the documentation at
https://docs.python.org/3/library/sys.html#sys.exit.

This indirectly prints some errors to stderr that previously went to
stdout.

Signed-off-by: Ulf Magnusson <Ulf.Magnusson@nordicsemi.no>

scripts/gen_priv_stacks.py

@@ -128,10 +128,9 @@ def main():
 
     thread_counter = eh.get_thread_counter()
     if thread_counter > max_threads:
-        sys.stderr.write("Too many thread objects (%d)\n" % thread_counter)
-        sys.stderr.write("Increase CONFIG_MAX_THREAD_BYTES to %d\n",
-                         -(-thread_counter // 8))
-        sys.exit(1)
+        sys.exit("Too many thread objects ({})\n"
+                 "Increase CONFIG_MAX_THREAD_BYTES to {}"
+                 .format(thread_counter, -(-thread_counter // 8)))
 
     with open(args.output, "w") as fp:
         write_gperf_table(fp, eh, objs)