execltp: fix scenario_group naming

Commit 9d5dac6 modified the folder name "scenario-groups" to
"scenario_groups" but it seems it missed changing it on
the execltp script as well.

Signed-off-by: Daniel Sangorrin <daniel.sangorrin@toshiba.co.jp>
Acked-by: Cyril Hrubis <chrubis@suse.cz>
diff --git a/execltp.in b/execltp.in
index 470a2dc..6d13ad1 100755
--- a/execltp.in
+++ b/execltp.in
@@ -307,7 +307,7 @@
 
     if len(args) == 0:
         # Default to scenarios also used by runltp.
-        fd = open(os.path.join(ltpdir, 'scenario-groups/default'), 'r')
+        fd = open(os.path.join(ltpdir, 'scenario_groups/default'), 'r')
         try:
             args = fd.readlines()
         finally: