Two bugs when scheduled space check

:Release Notes:
fixed two bugs when scheduled space check

:Detailed Notes:
1. activity manager didn't call spaceCheck every 5m
because of invalid luna call in activity-com.webos.mediadb.space.json
2. display wrong usedSize in mediadb partition because
if partition size is bigger than 2GB, displaying size is truncated.

:Testing Performed:
Compiled and tested localy.

:QA Notes:

:Issues Addressed:
[GF-59798] [DB8] Two bugs when scheduled space check

Open-webOS-DCO-1.0-Signed-off-by: kyouhyun.hwang <kyouhyun.hwang@lge.com>

Change-Id: Ia81964c3a40d9e70dffe6f71ff901e2f8ba5bffa
Reviewed-on: https://g2g.palm.com/4550
Reviewed-by: DCO Verification
Reviewed-by: Kyouhyun Hwang <kyouhyun.hwang@lge.com>
Tested-by: Kyouhyun Hwang <kyouhyun.hwang@lge.com>
Reviewed-by: Maksym Sditanov <maxim.sditanov@lge.com>
Reviewed-by: Oleksii Uratkin <oleksii.uratkin@lge.com>
Tested-by: Oleksii Uratkin <oleksii.uratkin@lge.com>