do_node_deploy() to use greenthreads

The commit c4f2f26ed introduced a new mechanism to run background tasks
in the conductor where it's possible to run some code synchronously
(e.g validations) and then spawn a greenthread that will do the real
work in the background (asynchronously), only one lock is acquired and
used for both tasks to avoid race conditions. This patch converts the
do_node_deploy() method to make use of this mechanism for deploying nodes.

Partial-Bug: #1285507
Change-Id: Ie03afd66d365e48c9dc3dc48f31e93a08e07e79f
Merge "do_node_deploy() to use greenthreads"