Fix multiple services registrations in luna-service2

:Release Notes:
Fixed handling of multiple simultaneous register requests to
luna-service2 hub

:Detailed Notes:
To fix simultaneous requests handling socket backlog was increased
from 10 to 30. Added new error code for EAGAIN errors occured during
connection to hub.

:Testing Performed:
Unit tests passed. Test case from JIRA ticked checked.

:QA Notes:

:Issues Addressed:
[GF-38721] Regarding 'backlog' in luna-service2 library

Open-webOS-DCO-1.0-Signed-off-by: Mykola Kryvonos <mykola.kryvonos@lge.com>

Change-Id: Iebb9c2a6d6e952404ad2a09e386ffaecb1de5b1f
Reviewed-on: https://g2g.palm.com/3600
Reviewed-by: Anatolii Sakhnik <anatolii.sakhnik@lge.com>
Reviewed-by: Mykola Kryvonos <mykola.kryvonos@lge.com>
Tested-by: Mykola Kryvonos <mykola.kryvonos@lge.com>