[subscriber] do not report future_error

It seems sometimes (maybe when objects are deleted earlier?)
subscription promise is not delivered to event processing function,
nothing can be done with it, so reporting does not help

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
[subscriber] try to open user or system file

First try to open file corresponding to user property, if it is failed,
try to open system one

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
[subscriber] try to access property again faster

At the beginning try to reaccess property with higher pace

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>