cache: Add defaults for intercepted command line arguments

Signed-off-by: Euan Harris <euan.harris@citrix.com>
cache: Add --debug option

Signed-off-by: Euan Harris <euan.harris@citrix.com>
cache: Add a salt which can be changed to invalidate the cache if the format changes

Signed-off-by: Euan Harris <euan.harris@citrix.com>