Release 5.5.2

Release 5.5.2

This version brings one major change - from now on buxton2ctl is used
instead of vconftool to dump the internal database (buxton is the
backend used by vconf anyway).  The reason for this change is
inefficency of vconftool utility, for details see commit 5991e4b
("dump_systemstate: Replace extremely inefficient vconftool with
buxton2ctl").

Minor improvements include:
 - util: Add fsync_path to selectively flush file buffer to disk
 - util: Fix and replace nullvec2str utility function with concatenate()
 - Define _GNU_SOURCE once for whole codebase
 - packaging: Drop unused variables from cmake invocation
 - util: Unify function calling convention to specify destination first
 - util: copy_bytes: Multiple changes

Change-Id: I260c34576783ee0dfa79c9b704939b943dfa0515