[dvs] Re-add copy_file method to DVS (sonic-net#1507)

I re-added the copy_file method that was removed in a recent refactor.
Buildimage tests depend on this method, so subsequent submodule updates will fail.

Signed-off-by: Danny Allen <[email protected]>

tests/conftest.py

@@ -9,6 +9,8 @@
 import string
 import subprocess
 import sys
+import tarfile
+import io
 
 from typing import Dict, Tuple
 from datetime import datetime
@@ -532,6 +534,17 @@ def runcmd(self, cmd: str) -> Tuple[int, str]:
 
         return (exitcode, out)
 
+    # used in buildimage tests, do not delete
+    def copy_file(self, path: str, filename: str) -> None:
+        tarstr = io.BytesIO()
+        tar = tarfile.open(fileobj=tarstr, mode="w")
+        tar.add(filename, os.path.basename(filename))
+        tar.close()
+
+        self.ctn.exec_run(f"mkdir -p {path}")
+        self.ctn.put_archive(path, tarstr.getvalue())
+        tarstr.close()
+
     def get_logs(self) -> None:
         log_dir = os.path.join("log", self.log_path) if self.log_path else "log"