Extend the retry backoff for machine ssh scp

In a real world scenario, this will work in the first iteration (maybe
the second after 2sec backoff), however the github workers are
particularly slow so extending this to make the tests pass.

Author: cderici

juju/machine.py

@@ -141,7 +141,7 @@ async def _scp(self, source, destination, scp_opts):
         # couple of times until either we run out of attempts, or the ssh command succeeds to
         # mitigate that effect.
         # TODO (cderici): refactor the ssh and scp subcommand processing into a single method.
-        retry_backoff = 1
+        retry_backoff = 2
         retries = 10
         for _ in range(retries):
             process = await jasyncio.create_subprocess_exec(*cmd)
@@ -185,7 +185,7 @@ async def ssh(
         # service is up and listening, which creates a race for the ssh command. So we retry a
         # couple of times until either we run out of attempts, or the ssh command succeeds to
         # mitigate that effect.
-        retry_backoff = 1
+        retry_backoff = 2
         retries = 10
         for _ in range(retries):
             process = await jasyncio.create_subprocess_exec(