respect VM_CORES/VM_MEMORY environment variables
respect VM_CORES/VM_MEMORY environment variables

[Finishes #100872484]

Signed-off-by: Emily Casey <2c35f9c4cdfaa4fb4d9df91b23e294fe59051836@pivotal.io>

cloudfoundry-incubator/lattice,cloudfoundry-incubator/lattice-release,cloudfoundry-incubator/lattice,cloudfoundry-incubator/lattice-release,cloudfoundry-incubator/lattice,cloudfoundry-incubator/lattice,cloudfoundry-incubator/lattice-release,cloudfoundry-incubator/lattice-release