SSH monitoring with sshkey and sshpassphrase on libssh fails

SSH monitoring, especially ssh.run, fails on Zabbix server or proxy which is built with libssh, and with keyfile and passphrase.

Some months ago, you change the default library from libssh2 to libssh. But ssh poller code has the bug for libssh for pubkey. It does not use passphrase. So, if keyfile require passphrase, ssh.run monitoring fails.

zabbix_server.log
Enter PEM pass phrase:
24894:20200721:200531.112 error reason for "Zabbix server:ssh.run["ssh passphrase test",192.168.122.80,,]" chan
ged: Failed to import private key: /etc/zabbix/ssh_key/id_rsa
Enter PEM pass phrase:

So, I fixed this bug and attached the patch.