elog-gen: handle empty template directories

In some cases, such as when building with meson, it is not useful
to separate the template directory for the template file when
invoking elog-gen.  Modify the template path handling code slightly
so that an empty template directory can be used with the template
file having the full path.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I26cae0f4af2fd03dfd194d593f40e9dedea9d012
diff --git a/tools/elog-gen.py b/tools/elog-gen.py
index 439beee..63b8969 100755
--- a/tools/elog-gen.py
+++ b/tools/elog-gen.py
@@ -137,10 +137,11 @@
         meta_yaml = get_meta_yaml_file(error_yaml)
 
         # Verify the input mako file
-        template_path = "/".join((i_template_dir, i_elog_mako))
+        template_path = os.path.join(i_template_dir, i_elog_mako)
         if (not (os.path.isfile(template_path))):
             print("Cannot find input template file " + template_path)
             exit(1)
+        template_path = os.path.abspath(template_path)
 
         get_elog_data(error_yaml,
                       meta_yaml,