[autotest] abstract_ssh: Fix usage of _make_scp_cmd

The input of _make_scp_cmd is changed from a list to a string in

36b6170 [autotest] Fix rsync command when retrieving multiple files.

Fix the usage in send_file.

BUG=chromium:588315
TEST=run audio_AudioBasicExternalMicrophone test

Change-Id: I9bc9aa693e57f65711952c31c3cd2e4c195cc1e0
Reviewed-on: https://chromium-review.googlesource.com/328857
Commit-Queue: Dan Shi <dshi@chromium.org>
Trybot-Ready: Dan Shi <dshi@chromium.org>
Tested-by: Dan Shi <dshi@chromium.org>
Reviewed-by: Dan Shi <dshi@chromium.org>
(cherry picked from commit 9b2812dc0fdeb762faa859586581cb4c18a34aea)
Reviewed-on: https://chromium-review.googlesource.com/330980
Reviewed-by: Cheng-Yi Chiang <cychiang@chromium.org>
Commit-Queue: Cheng-Yi Chiang <cychiang@chromium.org>
Tested-by: Cheng-Yi Chiang <cychiang@chromium.org>
1 file changed