Stylistic improvement of models.ComputeNodeStat

The patch is aimed at improving the readability of models.ComputeNodeStat.

Here, we rename the 'stats' attribute of the class to 'compute_node' (due to
the fact that the corresponding relation actually maps to ComputeNode class,
not to ComputeNodeStat). We also rewrite the relationship() method call to
make it stylistically conforming with the analogous 'service' relationship
in the ComputeNode class: we add the 'foreign_keys' parameter, wrap the
'backref' parameter into a method call and remove the auxiliary 'primary_join'
variable.

Change-Id: I2b1f27b4c1d06f364af01fc82d3490fd3bbf4ac0
Closes-Bug: #1215390
tenant_id implies all_tenants for servers list in V3 API

Makes tenant_id imply all_tenants is also enabled unless
explicitly disabled when a request is made for a list of
servers. This only occurs if the requestor is an admin. The
change is only made for the V3 API as although this behavior is
more intuitive it is too late to change it for the V2 API.

Change-Id: Ia84e62c8dc80ac3a2f16aee3620af31987cce570
Partial-Bug: 1185290
Catch exception while building due to instance being deleted

In run_instance() a instance_update() call in _start_building() can
result in a UnexpectedDeletingTaskStateError if the instance gets
deleted while being built.Since this is an expected situation, we
don't want this exception written in the logs or worse, the instance
be set to error state. Instead catch this and raise a proper
BuildAbortException that gets handled above this call.

Change-Id: Ib9d3dd22b33b104f1593d534876a5387df81d11c
Closes-Bug: #1223843
Add V3 API sample for server's actions

Adds api sample tests and api samples for server's actions

Partially implements blueprint v3-api-unittests

Change-Id: I4b420f09f9fc9a7f6fab8dbaeaa9b93631909255
XenAPI: Fix config section usage

Change I2e9f720ddce284fc112d6a5651fd277e6e31a17a introduced xenserver
sections but a couple of CONF variables were not updated to use the
new sections.

Fixed the few remaining options and add unit tests to ensure they are
caught in future.

The unit tests highlighted that the functions behaved strangely in
the cases where the default was being provided - so updated to be
clear about getting the default.

Closes-bug: 1253064

Change-Id: Ic538069cd087aa3cdc0a1f7fdb94820d5d3b22b1
Merge "Stylistic improvement of models.ComputeNodeStat"
Merge "Catch exception while building due to instance being deleted"
Merge "Add V3 API sample for server's actions"
Merge "tenant_id implies all_tenants for servers list in V3 API"
Merge "XenAPI: Fix config section usage"