[M120][WRTjs] Fix double dbus close issue

[M120][WRTjs] Fix double dbus close issue

Change the way to end dbus listening to fix double calls of
dbus_connection_close()

++
wrt-service application handling is not sensitive for
launch performance, so 500ms interval polling looks proper.
In fact, uv-task runner is polling as 500ms either.

Reference:
https://review.tizen.org/gerrit/#/c/platform/framework/web/chromium-efl/+/303807/

Change-Id: Icfcfc70a84333d3a8b8f1e0805bafee61b265bc8
Signed-off-by: DongHyun Song <dh81.song@samsung.com>
(cherry picked from commit d5b98c76536c01ba00086727620dbf71fcd331b0)
(cherry picked from commit 329f0ee54feb80e6c7f2af3efefb23f5a1f9f54b)