Switch to mksh as the default shell.

Switch the emulator builds to ash to make sure it still
works, in case we find that we need to go back to using ash.

Change-Id: Id5641940b63cc4225011be1c375f4c86ec4d21cc
diff --git a/core/config.mk b/core/config.mk
index 20a2582..3240e94 100644
--- a/core/config.mk
+++ b/core/config.mk
@@ -105,8 +105,8 @@
 # TODO: do symbol compression
 TARGET_COMPRESS_MODULE_SYMBOLS := false
 
-# Default shell is ash. Other possible value is mksh.
-TARGET_SHELL := ash
+# Default shell is mksh. Other possible value is ash.
+TARGET_SHELL := mksh
 
 # ###############################################################
 # Include sub-configuration files