integration tests

Fixes #9350

Change "usuable" to "usable".

Fix typo

`Propspective` -> `Prospective`

Added _meta hostvars key to gce.py plugin

Fixes #9333

* using inspect module instead of iteritems(self.__class__.__dict__, due
  to the fact that the later does not include attributes from parent
  classes
* added tags/when attributes to Base() class for use by all subclasses
* removed value/callable code from Attribute, as they are not used
* started moving some limited code from utils to new places in v2 tree
  (vault, yaml-parsing related defs)
* re-added ability of Block.load() to create implicit blocks from tasks
* started overhaul of Role class and role-related code

Detect docker as virtualization_type

Detect kvm guests through sys_vendor.

Typo: greatful -> grateful

Add integration test for the shell module

Add --pretty option for gce inventory plugin

New docker versions use "docker" in /proc/1/cgroup, which disturbs the
virtualization_type detection. So, grep for docker, in addition of
"lxc".

The two detection methods currently implemented do not cover all cases.

For example qemu guests invoked like this:
qemu -machine pc-i440fx-1.4,accel=kvm -cpu SandyBridge

return this information:
product_name: Standard PC (i440FX + PIIX, 1996)
cpuinfo: model name      : Intel Xeon E312xx (Sandy Bridge)

Add note on block properties

inventory for implementation