[api] AnalogProperty should always pull data

AnalogProperty always requests data from source when user reads file

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
[util] property_path_sys_default()

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
[consumer] starting to implement consumer c++ api

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
forward variadic arguments list properly

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
test .so linkage, related fixes

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
[util] pkgconfig file for statefs-util

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