[autotest] increase the detail of master-ssh connection death log

In order to better understand our flaky unexpected-master-ssh-death,
(in which the master connection socket file goes missing before the
process dies), it might be helpful to know whether the file alone
goes missing, or both the file and its containing temporary directory
go missing.

BUG=chromium:305641
TEST=None

Change-Id: Ia6d99734779c5be3196446e1de0123f6558da29a
Reviewed-on: https://chromium-review.googlesource.com/172421
Reviewed-by: Aviv Keshet <[email protected]>
Commit-Queue: Aviv Keshet <[email protected]>
Tested-by: Aviv Keshet <[email protected]>
1 file changed