getNTPTime() doesn't work

:Release Notes:
There is no ntpdate in webos-image, However, ntpdate is retired.
Changes ntpdate to sntp to get time offset from NTP server.

:Detailed Notes:
This commit depends on "webos-image: Add sntp from ntp=v4.2.6p5"
(https://g2g.palm.com/#/c/2801/)
That commit adds sntp in webos-image instead of ntpdate,
which has been deprecated.

luna-sysservice uses sntp in this commit.
so, this commit should be merged with other commit, which adds sntp.

:Testing Performed:
$ luna-send -n 1 -f luna://com.palm.systemservice/time/getNTPTime '{}'

expected result:
{
    "subscribed": false,
    "returnValue": true,
    "utc": 1372746542 //utc time must have value, not 0
}

:QA Notes:

:Issues Addressed:
[GF-10551] getNTPTime() doesn't work

Open-webOS-DCO-1.0-Signed-off-by: Youngeun Kim <ye0607.kim@lge.com>

Change-Id: I1957e13f4981d564206ab26d03f2c92de7fc8fe4
Reviewed-on: https://g2g.palm.com/2991
Reviewed-by: Build Verification
Reviewed-by: Youngeun Kim <ye0607.kim@lge.com>
Tested-by: Youngeun Kim <ye0607.kim@lge.com>
Reviewed-by: Roger Stringer <roger.stringer@lge.com>