[fuchsia] On scp error log scp command stdout and stderr for debugging.

The scp operations to retrieve test data from fuchsia VMs on arm64 machines have infrequent errors (about 1 out of 3,000 test suites fail this way).

This CL adds logging scp output on error to get more information about the fails.

Bug: 1050072
Change-Id: I36b88863e5b3e9f27f0b43ea16ab67509d9bf39a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2066489
Commit-Queue: Stephen Roe <steveroe@google.com>
Reviewed-by: Sergey Ulanov <sergeyu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#744147}

build/fuchsia/remote_cmd.py

@@ -130,4 +130,9 @@ class CommandRunner(object):
     scp_command += [dest]
 
     _SSH_LOGGER.debug(' '.join(scp_command))
-    subprocess.check_call(scp_command, stdout=open(os.devnull, 'w'))
+    try:
+      scp_output = subprocess.check_output(scp_command,
+                                           stderr=subprocess.STDOUT)
+    except subprocess.CalledProcessError as error:
+      _SSH_LOGGER.info(error.output)
+      raise