apache2: fix error messages when restart apache service

There are error messages when restart apache service:

Observed Behavior
======================
root@qemu0:/etc/php# apachectl restart
AH00557: httpd: apr_sockaddr_info_get() failed for qemu0
AH00558: httpd: Could not reliably determine the server's fully qualified domain name, using 127.0.0.1. Set the 'ServerName' directive        globally to suppress this message
root@qemu0:/etc/php# /etc/init.d/apache2 restart
AH00557: httpd: apr_sockaddr_info_get() failed for qemu0
AH00558: httpd: Could not reliably determine the server's fully qualified domain name, using 127.0.0.1. Set the 'ServerName' directive        globally to suppress this message
root@qemu0:/etc/php# /etc/init.d/apache2 stop
AH00557: httpd: apr_sockaddr_info_get() failed for qemu0
AH00558: httpd: Could not reliably determine the server's fully qualified domain name, using 127.0.0.1. Set the 'ServerName' directive        globally to suppress this message

Add 'ServerName localhost:80' to httpd.conf could fix this issue.

Signed-off-by: Hongxu Jia <hongxu.jia@windriver.com>