Sort out the logic of app id, and get exec path from pkgmgr

Two commits
The patch of app id I made some days ago make the logic of app
id become too complex, so I sort out the logic of app id:
For xpk, [app_id] = GenerateId or GenerateIdForPath,
             [tizen_app_id] = xwalk.[app_id]
For wgt, [app_id] = GenerateId([tizen_app_id])
             [tizen_app_id] = Get from config.xml
    
We always use [app_id] internal runtime, and [tizen_app_id] used
for tizen pkgmgr DB.

Ali cannot get app info after update an app, so we can get exec
path from pkgmgr to avoid this issue of ali.
    
BUG=XWALK-2189