tests/remote: Use a function to add a log file to a remote host

tests/remote: Use a function to add a log file to a remote host

Instead of accessing the logs list member of the remote host directly,
use a function to add logs to the remote host to be collected after the
test. This enables us to later have different implementation of remote
hosts or logs collection without requiring to have this list as the
implementation.

Signed-off-by: Jonathan Afek <jonathanx.afek@intel.com>