This commit switching tasks resolution approach to the tags based one.
Tag - minimal unit what's necessary only for task resolution and can be
mapped to the node through the role interface only. Each role provides set
of tags in its 'tags' field and may be modified via role API. Tag may be
created separately via tag API, but, this tag can not be used unless it's
stuck to the role.
Change-Id: Icd78fd124997c8aafb07964eeb8e0f7dbb1b1cd2
Implements: blueprint role-decomposition
2b0242f645