libgdbus: Add a context to handle pending event sources

libgdbus: Add a context to handle pending event sources

Add a context in dbus_handle to handle pending an event source after calling g_dbus_connection_close_sync().
This is because, g_dbus_connection_close_sync() adds an idle source to the context.
If this event source is not handled, then connection ref_cnt is not decremented.
It causes that the connection structures and the corresponding threads are left after free.

Change-Id: Ibc5597b26ef264e03fb86aef92d72627c7d2b8d1
Signed-off-by: Unsung Lee <unsung.lee@samsung.com>