[Build] Fix the build unstalbe issue caused by the kvm not ready (#12180) (#12354)

Why I did it
Fix the build unstable issue caused by the kvm 9000 port is not ready to use in 2 seconds.

2022-09-02T10:57:30.8122304Z + /usr/bin/kvm -m 8192 -name onie -boot order=cd,once=d -cdrom target/files/bullseye/onie-recovery-x86_64-kvm_x86_64_4_asic-r0.iso -device e1000,netdev=onienet -netdev user,id=onienet,hostfwd=:0.0.0.0:3041-:22 -vnc 0.0.0.0:0 -vga std -drive file=target/sonic-6asic-vs.img,media=disk,if=virtio,index=0 -drive file=./sonic-installer.img,if=virtio,index=1 -serial telnet:127.0.0.1:9000,server
2022-09-02T10:57:30.8123378Z + sleep 2.0
2022-09-02T10:57:30.8123889Z + '[' -d /proc/284923 ']'
2022-09-02T10:57:30.8124528Z + echo 'to kill kvm:  sudo kill 284923'
2022-09-02T10:57:30.8124994Z to kill kvm:  sudo kill 284923
2022-09-02T10:57:30.8125362Z + ./install_sonic.py
2022-09-02T10:57:30.8125720Z Trying 127.0.0.1...
2022-09-02T10:57:30.8126041Z telnet: Unable to connect to remote host: Connection refused

How I did it
Waiting more time until the tcp port 9000 is ready, waiting for 60 seconds in maximum.

Co-authored-by: xumia <[email protected]>

Author: liushilongbuaa

scripts/build_kvm_image.sh

@@ -48,6 +48,19 @@ prepare_installer_disk()
     umount $tmpdir
 }
 
+wait_kvm_ready()
+{
+    local count=30
+    local waiting_in_seconds=2.0
+    for ((i=1; i<=$count; i++)); do
+        sleep $waiting_in_seconds
+        echo "$(date) [$i/$count] waiting for the port $KVM_PORT ready"
+        if netstat -l | grep -q ":$KVM_PORT"; then
+          break
+        fi
+    done
+}
+
 create_disk
 prepare_installer_disk
 
@@ -78,7 +91,7 @@ trap on_error ERR
 
 kvm_pid=$!
 
-sleep 2.0
+wait_kvm_ready
 
 [ -d "/proc/$kvm_pid" ] || {
         echo "ERROR: kvm died."