Add new type of fault called "stress". When activated this fault
produces load on CPU, disk, memory or kernel of node. The functionality
is implemented with help of stress-ng utility.
Node collection API is extended:
def stress(self, target, duration=None)
Human API is extended, examples of commands:
* stress cpu for 20 seconds on controller.domain.tld node
* stress disk for 10 seconds on all nodes
* stress memory for 60 seconds on all nodes with keystone service
Change-Id: I8ddb2292b8dd19f476e4a5071259d1a90cbaa37c
Note: 'stress-ng' is required to be installed on target nodes.
9cf6337d5e