Allow subscription requests even if connman is not running

:Release Notes:
The subscribable APIs will now return '{"subscribed":true}', even if connman is not running.

:Detailed Notes:
The following APIs were earlier returning error on subscription requests when connman service
was unavailable:
com.palm.connectionmanager/getstatus
com.palm.wifi/getstatus
com.palm.wifi/findnetworks
com.palm.wifi/p2p/getpeers
com.palm.wifi/p2p/getgrouppeers

With this fix, now these APIs will just subscribe the callers, so that once connman service
become available and there is any response available, they will start sending the updates to
the callers.

:Testing performed:
Tested all the APIs to see the response with connman service not running and then with
the service running.

:Issues Addressed:
[GF-8052] ConnectionManager ignores subscription calls until ConnMan service is up

Open-webOS-DCO-1.0-Signed-off-by: Sapna Todwal <sapna.todwal@lge.com>

Change-Id: I509cb21d9dc9e08f5588856a0af50f8330618530
Reviewed-on: https://g2g.palm.com/2909
Reviewed-by: Build Verification
Reviewed-by: Simon Busch <simon.busch@lge.com>
Reviewed-by: Sapna Todwal <sapna.todwal@lge.com>
Tested-by: Sapna Todwal <sapna.todwal@lge.com>