update-utmp: wait slightly longer for the private bus socket being active

update-utmp: wait slightly longer for the private bus socket being active

Before a339495b1d67f69f49ffffdd96002164a28f1c93, update-utmp typically
connects the public DBus socket when disconnected from the private DBus
socket, as dbus service should be active even during PID1 is being reexecuted.

However, after a339495b1d67f69f49ffffdd96002164a28f1c93, update-utmp
tries to connect only the private DBus socket, but reexecution of PID1
may be slow, hence all trials may fail when the reexecution is slow.

With this change, now it waits for 100ms to 2000ms, so in total it waits
about 37 seconds in average, previously about 4 seconds.