Change ="DOWN" to !="UP" for correct status detection in ping_host.sh

If a IP is added to the pkgpinghost file no status file exists in
/var/db/pingstatus, so $PREVIOUSSTATUS can never be equal to "DOWN" or
"UP"
To correct this, test for not equal to opposite
add if(file_exists("{$g['varrun_path']}/booting")  to test for system booting

During startup_packages the variable booting is false but system is
still booting.
But file booting is still pressent