CA-142107: Remove misleading use of Xenguest when logging failures

Signed-off-by: Si Beaumont <simon.beaumont@citrix.com>
Correct spelling (s/exitted/exited) in log message

Signed-off-by: Si Beaumont <simon.beaumont@citrix.com>
CA-142107: Improve logging in cancellable_subprocess

Signed-off-by: Si Beaumont <simon.beaumont@citrix.com>
CA-142107: Log conversion script process exiting

Signed-off-by: Si Beaumont <simon.beaumont@citrix.com>
Merge pull request #126 from simonjbeaumont/ca-142107-2

CA-142107 #2: Improve logging around migration script