[format] Add CGroup Manager in form of optional "plugin"

-  Move all Computer attribute initialization into Computer constructor
-  Rename 'construct' to 'format' because we are in slap.format
-  Introduce Manager base class
-  Implement CGroupManager to take care of cgroup's cpuset

slapos/README.format.txt

-format
+Format
 ======
 
-slapformat is an application to prepare SlapOS ready node (machine).
+slapformat is an application to prepare SlapOS-ready node to be used inside SlapGrid Cloud.
 
 It "formats" the machine by:
 
@@ -10,9 +10,21 @@ It "formats" the machine by:
  - creating needed tap interfaces
  - creating TUN interfaces
  - creating needed directories with proper ownership and permissions
+ - (optional-manager) creating cgroup resource tree for slapos
 
-In the end special report is generated and information are posted to
-configured SlapOS server.
+It reads configuration from /etc/opt/slapos/slapos.cfg and formats computer
+accordingly. The variables are number of partitions, IP addresses, storages
+and network interfaces.
+
+Format uploads a into configured SlapOS Master server.
+
+Format dumps allocated resources for the partition into a JSON file per 
+partition ~/.slapos-resource. This file contains network interfaces, 
+IP address ranges and port ranges. The resource constraints can be 
+recursively folded. 
+
+Pluggable parts for formatting are available too. They are called Managers
+and can be turned on/off via configuration property manager_list.
 
 This program shall be only run by root.