ktest: Evaluate variables entered on the command line

When ktest.pl is called without any arguments, or if the config
file does not exist, ktest.pl will ask the user for some information.
Some of these questions are code paths. Allowing the user to type
${PWD} for the current directory greatly simplifies these entries.

Add variable processing to the entered values.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>