Replace unsafe characters in SET_HOSTNAME.

When setting the hostname from $SET_HOSTNAME, replace any characters
not allowed in hostnames (as specified in RFC 952) with a hyphen.
This is enables a VM template to safely use the VM's name as the
hostname (by setting the context variable SET_HOSTNAME=$NAME).

base_arch/etc/one-context.d/05-hostname

@@ -20,7 +20,7 @@ function get_dns_name() {
 }
 
 if [ -n "$SET_HOSTNAME" ]; then
-    set_hostname $SET_HOSTNAME
+    set_hostname $(echo "$SET_HOSTNAME" | sed -e 's/[^-a-zA-Z0-9]/-/g')
 elif [ -n "$DNS_HOSTNAME" ]; then
     set_hostname $(get_dns_name)
 fi

base_deb.one/etc/one-context.d/05-hostname

@@ -22,7 +22,7 @@ function get_dns_name() {
 }
 
 if [ -n "$SET_HOSTNAME" ]; then
-    set_hostname $SET_HOSTNAME
+    set_hostname $(echo "$SET_HOSTNAME" | sed -e 's/[^-a-zA-Z0-9]/-/g')
 elif [ -n "$DNS_HOSTNAME" ]; then
     set_hostname $(get_dns_name)
 fi

base_rpm.one/etc/one-context.d/05-hostname

@@ -23,7 +23,7 @@ function get_dns_name() {
 }
 
 if [ -n "$SET_HOSTNAME" ]; then
-    set_hostname $SET_HOSTNAME
+    set_hostname $(echo "$SET_HOSTNAME" | sed -e 's/[^-a-zA-Z0-9]/-/g')
 elif [ -n "$DNS_HOSTNAME" ]; then
     set_hostname $(get_dns_name)
 fi