ubuntu_k8s_unit_tests sub tests failed to build with gcc: cannot allocate memory on X-4.15-GCP

This is not a regression, we have changed how we run this test for different releases in this commit:
https://git.launchpad.net/~canonical-kernel-team/+git/autotest-client-tests/commit/?id=e4b72827b7bf6dd402443b59e2d11a83ab3a749a

Test failed on:
  * g1-small
  * n1-highcpu-4

Some tests will failed to build on them, e.g.:
  FAIL k8s.io/kubernetes/cmd/hyperkube [build failed]
  FAIL k8s.io/kubernetes/cmd/kube-apiserver/app [build failed]
  FAIL k8s.io/kubernetes/cmd/kubelet/app [build failed]
  FAIL k8s.io/kubernetes/cmd/kube-proxy/app [build failed]
  FAIL k8s.io/kubernetes/cmd/libs/go2idl/client-gen/testoutput/clientset_generated/test_internalclientset [build failed]
  FAIL k8s.io/kubernetes/contrib/mesos/cmd/km [build failed]

Different tests will fail on different instances.

Looks like they all failed with:
  /usr/lib/go-1.6/pkg/tool/linux_amd64/link: running gcc failed: fork/exec /usr/bin/gcc: cannot allocate memory