At present, the diag tool uses its default purge file. However, users
may find it beneficial to specify and reuse their own purge file. A new
command line option, --purge, has been introduced to allow users to
provide their own purge file to diag. When this option is used, the
default purge file is ignored.
Signed-off-by: Frantisek Hrbata <frantisek.hrbata@espressif.com>