added Buildkite pipeline and integration tests

This pipeline contains the tests that are currently run for
kvm-ioctls. The pipeline also has a step that runs the coverage
test defined in integration_tests/test_coverage.py.

The purpose of this pipeline is to be used by all rust-vmm
repositories to ensure we keep the same quality bar for all crates.

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

coverage_config.json.sample

@@ -0,0 +1,5 @@
+{
+  "coverage_score": 90,
+  "exclude_path": "my_autogenerated_file.rs,second_file.rs",
+  "crate_features": "my_dummy_feature,dummy_feature2"
+}