Merge branch 'httpapi-client'

This branch provides Boruta REST API client package. It implements
Requests and Workers interfaces, and provides additional convenient
methods to check request/worker state or request timeout. This package
is meant for services that want to use Boruta as its device farm (e.g.
Weles).

Change-Id: I2b116abdcb924f7443fad1c4c5401ba71d8d24fa