tools: support for deprecating config values.

- each config value can be deprecated via setting its property
'.deprecated' to true. If not specified, deprecated=false is assumed.

- when someone tries to set deprecated value, following message is
printed: "ConfigKey <option_name> is deprecated. Please
refer to product documentation."

Change-Id: I636f7fe2530acfe00d8f0487001ddc781d1745a0
Signed-off-by: Martin Mucha <mmucha@redhat.com>