layers: Return an error when generator scripts fail.

Currently the scripts would abort with an error message, but not an OS
error code. Adding an error code allows build systems to correctly
detect the script failure as a failed build step.

Change-Id: I142a6215a3c02e6a880bfce0c3aba2c3c8fc4ff1
diff --git a/scripts/parameter_validation_generator.py b/scripts/parameter_validation_generator.py
index 032b9fd..85078a6 100644
--- a/scripts/parameter_validation_generator.py
+++ b/scripts/parameter_validation_generator.py
@@ -201,7 +201,7 @@
                 break
         if self.vuid_file == None:
             print("Error: Could not find vk_validation_error_messages.h")
-            quit()
+            sys.exit(1)
     #
     # Generate Copyright comment block for file
     def GenerateCopyright(self):
@@ -246,7 +246,7 @@
     def IdToHex(self, dec_num):
         if dec_num > 4294967295:
             print ("ERROR: Decimal # %d can't be represented in 8 hex digits" % (dec_num))
-            sys.exit()
+            sys.exit(1)
         hex_num = hex(dec_num)
         return hex_num[2:].zfill(8)
     #