ktest: Add DEFINED keyword for IF statements

Have IF statements process if a config variable or option has been
defined or not. Can use NOT DEFINED in the case for telling if
a variable or option has not been defined.

DEFAULTS IF NOT DEFINED SSH_USER
SSH_USER = root

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
diff --git a/tools/testing/ktest/sample.conf b/tools/testing/ktest/sample.conf
index 0fd3ca3..7b49f07 100644
--- a/tools/testing/ktest/sample.conf
+++ b/tools/testing/ktest/sample.conf
@@ -137,6 +137,23 @@
 # ELSE
 # BUILD_TYPE = useconfig:${CONFIG_DIR}/config-64
 #
+# The DEFINED keyword can be used by the IF statements too.
+# It returns true if the given config variable or option has been defined
+# or false otherwise.
+#
+# 
+# DEFAULTS IF DEFINED USE_CC
+# CC := ${USE_CC}
+# ELSE
+# CC := gcc
+#
+#
+# As well as NOT DEFINED.
+#
+# DEFAULTS IF NOT DEFINED MAKE_CMD
+# MAKE_CMD := make ARCH=x86
+#
+#
 #
 # INCLUDE file
 #