envoy: Pass BAZEL_BUILD_OPTS to bazel test as well.
envoy: Pass BAZEL_BUILD_OPTS to bazel test as well.

Otherwise `make tests` invalidates the bazel cache, also for a subsequest `make`.

Reported-by: Ray Bejjani <7f525154e857f3d57a641a83dddc584f42addc6a@covalent.io>
Signed-off-by: Jarno Rajahalme <0f1ab0ac7dffd9db21aa539af2fd4bb04abc3ad4@covalent.io>

tgraf/cilium,michi-covalent/cilium,tklauser/cilium,scanf/cilium,eloycoto/cilium,scanf/cilium,eloycoto/cilium,eloycoto/cilium,eloycoto/cilium,tklauser/cilium,eloycoto/cilium,michi-covalent/cilium,cilium/cilium,tklauser/cilium,scanf/cilium,cilium/cilium,cilium/cilium,michi-covalent/cilium,cilium-team/cilium,tgraf/cilium,tgraf/cilium,tklauser/cilium,cilium/cilium,tgraf/cilium,cilium-team/cilium,tklauser/cilium,eloycoto/cilium,eloycoto/cilium,scanf/cilium,cilium/cilium,michi-covalent/cilium,scanf/cilium,scanf/cilium,tgraf/cilium,tgraf/cilium,michi-covalent/cilium,scanf/cilium