Added Buildkite CI

It's easier to test this with the rust-vmm-ci directly as it already
runs all the basic tests.

Signed-off-by: Andreea Florescu <fandree@amazon.com>

.gitmodules

@@ -0,0 +1,3 @@
+[submodule "rust-vmm-ci"]
+	path = rust-vmm-ci
+	url = https://github.com/rust-vmm/rust-vmm-ci.git

coverage_config.json

@@ -0,0 +1 @@
+{"coverage_score": 93.1, "exclude_path": "", "crate_features": ""}