proxy: add multi-nodes support.

slapos/proxy/schema.sql

---version:10
-CREATE TABLE IF NOT EXISTS software%(version)s (url VARCHAR(255) UNIQUE);
+--version:11
+CREATE TABLE IF NOT EXISTS software%(version)s (
+  url VARCHAR(255),
+  computer_reference VARCHAR(255) DEFAULT 'computer',
+  CONSTRAINT uniq PRIMARY KEY (url, computer_reference)
+);
+
 CREATE TABLE IF NOT EXISTS computer%(version)s (
+  reference VARCHAR(255),
   address VARCHAR(255),
   netmask VARCHAR(255),
-  CONSTRAINT uniq PRIMARY KEY (address, netmask));
+  CONSTRAINT uniq PRIMARY KEY (reference)
+);
 
 CREATE TABLE IF NOT EXISTS partition%(version)s (
-  reference VARCHAR(255) UNIQUE,
+  reference VARCHAR(255),
+  computer_reference VARCHAR(255) DEFAULT 'computer',
   slap_state VARCHAR(255) DEFAULT 'free',
   software_release VARCHAR(255),
   xml TEXT,
@@ -16,11 +24,13 @@ CREATE TABLE IF NOT EXISTS partition%(version)s (
   partition_reference VARCHAR(255),
   requested_by VARCHAR(255), -- only used for debugging,
                              -- slapproxy does not support proper scope
-  requested_state VARCHAR(255) NOT NULL DEFAULT 'started'
+  requested_state VARCHAR(255) NOT NULL DEFAULT 'started',
+  CONSTRAINT uniq PRIMARY KEY (reference, computer_reference)
 );
 
 CREATE TABLE IF NOT EXISTS slave%(version)s (
-  reference VARCHAR(255) UNIQUE,
+  reference VARCHAR(255),
+  computer_reference VARCHAR(255),
   connection_xml TEXT,
   hosted_by VARCHAR(255),
   asked_by VARCHAR(255) -- only used for debugging,
@@ -29,6 +39,7 @@ CREATE TABLE IF NOT EXISTS slave%(version)s (
 
 CREATE TABLE IF NOT EXISTS partition_network%(version)s (
   partition_reference VARCHAR(255),
+  computer_reference VARCHAR(255),
   reference VARCHAR(255),
   address VARCHAR(255),
   netmask VARCHAR(255)