Up until now components were simple objects decoupled from fabric
execution. Their methods were just returning a list of bash commands
which utils module was executing in the correct context.

This patch changes this rational. Specifically:

A Component() gets initialized with an execution context that is a
configuration snapshot of the target setup, cluster and node. A
component implements the following helper methods: check, install,
prepare, configure, restart, initialize, and test. All those methods
will be executed on the target node with this order during setup.

Additionally each Component class implements admin_pre, and
admin_post methods which invoke actions on different components on
the same execution context before and after installation. For
example before a backend gets installed, its FQDN must resolve to
the master floating IP, so we have to run some actions on the ns
node and after installation we must add it to cyclades (snf-manage
backend-add on the cyclades node).

Component() inherits ComponentRunner() which practically exports the
setup() method. This will first check if the required components are
installed, will install them if not and update the status of target
node.

ComponentRunner() inherits FabricRunner() which practically wraps
basic fabric commands (put, get, run) with the correct execution
environment.

The fabfile practically gets the target nodes for each role from the
configuration and uses the roles module which knows the
role-component mapping to get the target component with the proper
execution context. Then it just invokes the setup() method.

Each component gets initialized with an execution context and uses
the config module for accessing global wide options. The context
provides node, cluster, and setup related info.

We introduce some helper decorators that wrap methods of Component
class and update its execution context (self, self.ctx):

- parse_* executes the wrapped method and parses the output.
  The desired vars (user_id, backend_id, user_uuid, etc.) are
  stored in the execution context and made available to other
  methods.

- update_admin initializes the admin roles (NS, Astakos,
  Cyclades, etc.) of the current context and make them available
  under self.NS, self.ASTAKOS, etc. These have the same execution
  context of the current components besides the target node
  which gets derived from the corresponding config.

- update_cluster_admin initializes the cluster's admin role
  and make it available under self.MASTER.

- run_cmds runs the list of returned commands in the target node

The update_ns() method of NS component gets the
self.ctx.admin_fqdn and invokes nsupdate accordingly.

Signed-off-by: Dimitris Aragiorgis <dimara@grnet.gr>