add coverage file

The file is needed by the rust-vmm-ci coverage integration test.

Signed-off-by: Andreea Florescu <[email protected]>

Author: andreeaflorescu

coverage_config_x86_64.json

@@ -0,0 +1,5 @@
+{
+  "coverage_score": 91.6,
+  "exclude_path": "",
+  "crate_features": ""
+}