kdumpctl: echo msg when waiting for connection

Print some message during the long wait period to reflect the process.
The message will look like:

  Network dump target is not usable, waiting for it to be ready
  ...

Signed-off-by: Pingfan Liu <piliu@redhat.com>
Acked-by: Kairui Song <kasong@redhat.com>

kdumpctl

@@ -736,6 +736,7 @@ check_ssh_config()
 check_and_wait_network_ready()
 {
 	local start_time=$(date +%s)
+	local warn_once=1
 	local cur
 	local diff
 	local retval
@@ -760,6 +761,12 @@ check_and_wait_network_ready()
 			return 1
 		fi
 
+		if [ $warn_once -eq 1 ]; then
+			echo "Network dump target is not usable, waiting for it to be ready"
+			warn_once=0
+		fi
+		echo -n .
+
 		cur=$(date +%s)
 		let "diff = $cur - $start_time"
 		# 60s time out