kdump test: output more useful info for users aware of

Resolves: RHEL-96907
Resolves: RHEL-96289

This patch have no functional change for kdumpctl test, but let it
output more info to let users know.

1) Let "kdumpctl restart" to output the kdump test status:

    $ kdumpctl restart
    kdump: kexec: unloaded kdump kernel
    kdump: Stopping kdump: [OK]
    kdump: kexec: loaded kdump kernel
    kdump: Starting kdump: [OK]
    kdump: Notice: No vmcore creation test performed!

2) Output stderr when "reload" fails, which can help user to identify
   the failing root cause:

    $ echo 1 > /proc/sys/kernel/kexec_load_disabled
    $ kdumpctl test
    DANGER!!! Will perform a kdump test by crashing the system, proceed? (y/N):
    kdump: Start kdump test...
    kexec_file_load(unload) failed: Operation not permitted
    kdump: kexec: failed to unload kdump kernel
    kdump: Stopping kdump: [FAILED]
    kdump: Set kdump test id fail.

Signed-off-by: Tao Liu <[email protected]>

Author: liutgnu

kdumpctl

@@ -1714,7 +1714,7 @@ set_kdump_test_id()
 
 	KDUMP_COMMANDLINE_APPEND+=" $_id "
 
-	if ! reload >&/dev/null; then
+	if ! reload > /dev/null; then
 		derror "Set kdump test id fail."
 		exit 1
 	fi
@@ -1931,6 +1931,7 @@ main()
 			derror "Starting kdump: [FAILED]"
 			exit 1
 		fi
+		check_vmcore_creation_status
 		;;
 	rebuild)
 		rebuild