Dynamic volume allocation

As a user I can set partitioning schema in a data-driven way, without need to create schema for specific hardware.
For example I may have a schema for storage, and I can apply it to any hardware (amount of disks with different sizes).

Specification [1]

List of problems/edge cases, which should be validated after development:
* Min size should be easily changed (https://bugs.launchpad.net/fuel/+bug/1266569)
* Confusion between min and optimal sizes (https://bugs.launchpad.net/fuel/+bug/1266569)
* Validate that schema is correct on each update (https://bugs.launchpad.net/fuel/+bug/1453885)
* Combination of `full-disk` and `all` causes problems (https://bugs.launchpad.net/fuel/+bug/1466428)
* Not all space is allocated by default (https://bugs.launchpad.net/fuel/+bug/1295717, https://bugs.launchpad.net/fuel/+bug/1490597)
* Don’t allocate a single volume on ssd and hdd
* Boot partition configuration (exclude raid https://bugs.launchpad.net/fuel/+bug/1258347 [is it really fixed?])

Original bp: https://blueprints.launchpad.net/fuel/+spec/volume-manager-refactoring

[1] https://github.com/openstack/fuel-specs/blob/master/specs/7.0/volume-manager-refactoring.rst#dynamic-allocation