Coverage test: keep stdin open

Pytest closes stdin by default, so any processes
spawned from it won't have it. As some tests in
various rust-vmm crates might need stdin to be
open, we mock it with a (currently empty) byte
stream, which we can extend in the future.

Signed-off-by: Alexandra Iordache <aghecen@amazon.com>

integration_tests/test_coverage.py

@@ -79,7 +79,9 @@ def _get_current_coverage(coverage_config):
         exclude_pattern
     )
 
-    subprocess.run(kcov_cmd, shell=True, check=True)
+    # Pytest closes stdin by default, but some tests might need it to be open.
+    # In the future, should the need arise, we can feed custom data to stdin.
+    subprocess.run(kcov_cmd, shell=True, check=True, input=b'')
 
     # Read the coverage reported by kcov.
     coverage_file = os.path.join(kcov_output_dir, 'index.js')