Use configure option yaml path to generate elog-errors.hpp

Add a config variable that can be passed via a recipe to
point the parser to a directory where the error yaml files are.
Rename elog-gen.hpp to elog-errors.hpp, which better matches the
exception error log file names.
Include elog-gen.hpp in elog.hpp so that callers that need to
create and commit error logs only need to include one header file.

Change-Id: Ie3cd65ac761c1f7b2c99c50a2273859283a5ab4b
Signed-off-by: Adriana Kobylak <anoo@us.ibm.com>
diff --git a/tools/elog-gen.py b/tools/elog-gen.py
index 1a79139..360ae11 100755
--- a/tools/elog-gen.py
+++ b/tools/elog-gen.py
@@ -238,8 +238,8 @@
                       help="input mako template file to use")
 
     parser.add_option("-o", "--output", dest="output_hpp",
-                      default="elog-gen.hpp",
-                      help="output hpp to generate, elog-gen.hpp is default")
+                      default="elog-errors.hpp",
+                      help="output hpp to generate, elog-errors.hpp default")
 
     parser.add_option("-y", "--yamldir", dest="yamldir",
                       default="None",