Implement get/set property via property service

The property service is running inside the android init daemon and
creates a socket in /dev/socket/property_service which we can use
for setting properties (getting is done via an extra android patch
to add 'get' and 'list' support in the property service).

Also separated the get/set calls in a different library, so it can be
used by external applications without necessarily depending on
hybris-common.

Additional patches for the Android init system can be found at
http://people.canonical.com/~rsalveti/properties/

Based on a similar patch by Simon Busch <morphis@gravedo.de>.

Signed-off-by: Ricardo Salveti de Araujo <ricardo.salveti@canonical.com>