ktest: Allow options to be used by other options

There are cases where one ktest option may be used within another
ktest option. Allow them to be reused just like config variables
but there are evaluated at time of test not config processing time.

Thus having something like:

MAKE_CMD = make ARCH=${ARCH}

TEST_START
ARCH = powerpc

TEST_START
ARCH = arm

Will have the arch defined for each test iteration.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
diff --git a/tools/testing/ktest/sample.conf b/tools/testing/ktest/sample.conf
index 761079e..48cbcc80 100644
--- a/tools/testing/ktest/sample.conf
+++ b/tools/testing/ktest/sample.conf
@@ -133,6 +133,36 @@
 # the MAKE_CMD option will be evaluated by the shell when
 # the MAKE_CMD option is passed into shell processing.
 
+#### Using options in other options ####
+#
+# Options that are defined in the config file may also be used
+# by other options. All options are evaulated at time of
+# use (except that config variables are evaluated at config
+# processing time).
+#
+# If an ktest option is used within another option, instead of
+# typing it again in that option you can simply use the option
+# just like you can config variables.
+#
+# MACHINE = mybox
+#
+# TEST = ssh root@${MACHINE} /path/to/test
+#
+# The option will be used per test case. Thus:
+#
+# TEST_TYPE = test
+# TEST = ssh root@{MACHINE}
+#
+# TEST_START
+# MACHINE = box1
+#
+# TEST_START
+# MACHINE = box2
+#
+# For both test cases, MACHINE will be evaluated at the time
+# of the test case. The first test will run ssh root@box1
+# and the second will run ssh root@box2.
+
 #### Mandatory Default Options ####
 
 # These options must be in the default section, although most