Add fork arg to shell_cmd

- Add support for a fork argument to the shell_cmd function.
- Also, some minor comment formatting changes to other gen_x.py files.

Change-Id: I71553793591086da2548d52dcac4d80e208755b0
Signed-off-by: Michael Walsh <micwalsh@us.ibm.com>
diff --git a/lib/gen_valid.py b/lib/gen_valid.py
index f41c9cd..0c990b0 100755
--- a/lib/gen_valid.py
+++ b/lib/gen_valid.py
@@ -91,7 +91,7 @@
     - If the error_message contains a value:
         - Print the error_message as part of a full error report.
         - If global exit_on_error is set, then exit the program with a return
-        code of 1.
+          code of 1.
         - If exit_on_error is not set, return False.
 
     This function is designed solely for use by wrapper functions in this file