[inout] implementation of inout loader

Implementation of inout/mirror loader. This loader uses statefs
configuration files as a source of information to create input and
output namespaces with data written to files in the input namespace just
appeared in correponding files in the output namespace

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
conf file name format should be specific only in cache

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