Use number of cores to make a good assumption on number of threads to…

[baldersheim]

… use for content layer.
@vekterli PR

[vekterli]

👍 content model changes look good to me. I don't have the deepest insight into the flavor and provisioning code, so someone else might want to take a look at those changes (@bratseth ?).

[vekterli]

Travis failure:

[INFO] --- abi-check-plugin:7-SNAPSHOT:abicheck (default) @ config-provisioning ---
[ERROR] Class com.yahoo.config.provision.HostSpec: Extra method public void <init>(java.lang.String, java.util.List, com.yahoo.config.provision.Flavor)

[bratseth]

LGTM!