Cleanup SConscript
- Define functions to remove no-exception flags
- Define functions to add test-cases
- Re-org top level agent SConscript to define variables for common and
  test specific libraries
- Disable test cases that fail often
- Split netlink functionality in KSync to different library libksyncnl
- Make modules pkt, services, dns optional

Change-Id: I875fa3de1b45b39f8c0973385dbc1ec6d77d6d55