Since there are two implementations of runc and containerd that may
not always be in sync, the docker variant, and the opencontainers
variable, we create a virtual/* namespace for these components.
Anything requiring runc or containerd should set a preferred provider
to get the desired/tested variant.
We set the default provider to the docker variants, since they are
the primary use case for these components.
Signed-off-by: Bruce Ashfield <bruce.ashfield@windriver.com>