add support for sharing fd and pool with clients

add support for sharing fd and pool with clients

This adds two new API functions, which can be used for sharing
kdbus fd and kdbus pool with the library clients.

Until now, the library created its own connection each time
it was initialized, effectively allocating 1MB of memory
only for getting small responses to one of kdbus ioctls.

This kind of activity may be performed on any usable kdbus
connection. Thus, the idea of sharing existing connections
with libdbuspolicy.

As it is a change of interface (two new API functions), the version
of library and package has been bumped up.

Change-Id: I7bae7a60a386f1c3bc35c88528c9f2baa2c57e34