[build] configure multiarch and user session

rpmbuild --with-multiarch and --with(without)-usersession. Also users
gid is not hardcoded but detected in compile time

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