This change adds executor support for generic build resources.
Using the connection_port, a kube config file is generated to enable ansible
tasks to use the resource. Context and pod name is also exported in a
zuul.resources variable to enable job direct access to the build resource.
Currently this change supports 'kubectl' resource for containers that behave
like a machine, and 'project'/'namespace' resource for native containers.
Change-Id: Icdb9e800177dc770c58f65b02456a6b904be0666
Tristan Cacqueray