Block all signals before syslog call

:Release Notes:
Block all signals before syslog call

:Detailed Notes:
Syslog has internal non-recursive mutex. When syslog in interrupted by a
signal and signal hanlder writes a measage to the log, it leads to a deadlock
inside a syslog call
Prevent process being blocked by a syslog in a signal handler

:Testing Performed:
TV booted successfully with debug level for default context

:QA Notes:

:Issues Addressed:
[CMB-1565] Setting log level for default context to debug prevents a full startup

Open-webOS-DCO-1.0-Signed-off-by: Alekseyev Oleksandr<alekseyev.oleksandr@lge.com>

Change-Id: I620177ac71688b20ccd7eb561b2dba0669f0248c
Reviewed-on: https://g2g.lgsvl.com/6492
Reviewed-by: DCO Verification
Reviewed-by: Alekseyev Oleksandr <alekseyev.oleksandr@lge.com>
Tested-by: Alekseyev Oleksandr <alekseyev.oleksandr@lge.com>
Reviewed-by: Anatolii Sakhnik <anatolii.sakhnik@lge.com>
Merge remote-tracking branch 'origin/develop'

Open-webOS-DCO-1.0-Signed-off-by: Anatolii Sakhnik <anatolii.sakhnik@lge.com>