Change ping .. > nul to sleep (#647)

* Change `ping .. > nul` to `sleep`

The filename `nul` is a Windows-ism that causes the update script to
create such a file in the current working directory. The `ping`
utility is also an dependency not installed by
`installdependencies.sh`, so it seemed easier to change it to the
standard `sleep` command.

* Update dotnet-install script as requested by test

* Update dotnet-install.ps1

Co-authored-by: Tingluo Huang <tingluohuang@github.com>

src/Misc/layoutbin/update.sh.template

@@ -28,13 +28,13 @@ date "+[%F %T-%4N] Waiting for $runnerprocessname ($runnerpid) to complete" >> "
 while [ -e /proc/$runnerpid ]
 do
     date "+[%F %T-%4N] Process $runnerpid still running" >> "$logfile" 2>&1
-    ping -c 2 127.0.0.1 >nul
+    sleep 2
 done
 date "+[%F %T-%4N] Process $runnerpid finished running" >> "$logfile" 2>&1
 
 # start re-organize folders
 date "+[%F %T-%4N] Sleep 1 more second to make sure process exited" >> "$logfile" 2>&1
-ping -c 2 127.0.0.1 >nul
+sleep 1
 
 # the folder structure under runner root will be
 # ./bin -> bin.2.100.0 (junction folder)