start_instance script fails when installing

[ellieLitwack]

Steps to reproduce:

1. Run start_instance --ssh-keypath <SSH_KEYPATH> skynet-test Where <SSH_KEYPATH> is a file path that points to a ssh key.

Results:
The script runs successfully until the step Setting Docker configuration on the remote daemon.... Then, it produces this error:

Error creating machine: Error running provisioning: ssh command error:
command : sudo systemctl -f start docker
err     : exit status 1
output  : Job for docker.service failed because the control process exited with error code. See "systemctl status docker.service" and "journalctl -xe" for details.

When ssh'd into the newly created instance, running systemctl status docker.service produces:

● docker.service - Docker Application Container Engine
   Loaded: loaded (/lib/systemd/system/docker.service; enabled; vendor preset: enabled)
  Drop-In: /etc/systemd/system/docker.service.d
           └─10-machine.conf
   Active: inactive (dead) (Result: exit-code) since Wed 2017-07-05 19:07:31 UTC; 2min 37s ago
     Docs: https://docs.docker.com
  Process: 5209 ExecStart=/usr/bin/docker daemon -H tcp://0.0.0.0:2376 -H unix:///var/run/docker.sock --storage-driver aufs --tlsverify --tlscacert /etc/docker/ca.pem --tlscert 
 Main PID: 5209 (code=exited, status=1/FAILURE)

Jul 05 19:07:31 skynet-test systemd[1]: Failed to start Docker Application Container Engine.
Jul 05 19:07:31 skynet-test systemd[1]: docker.service: Unit entered failed state.
Jul 05 19:07:31 skynet-test systemd[1]: docker.service: Failed with result 'exit-code'.
Jul 05 19:07:31 skynet-test systemd[1]: docker.service: Service hold-off time over, scheduling restart.
Jul 05 19:07:31 skynet-test systemd[1]: Stopped Docker Application Container Engine.
Jul 05 19:07:31 skynet-test systemd[1]: docker.service: Start request repeated too quickly.
Jul 05 19:07:31 skynet-test systemd[1]: Failed to start Docker Application Container Engine.

and running journalctl -xe produces:

-- The start-up result is done.
Jul 05 19:09:44 skynet-test systemd[5218]: Startup finished in 8ms.
-- Subject: System start-up is now complete
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
-- 
-- All system services necessary queued for starting at boot have been
-- successfully started. Note that this does not mean that the machine is
-- now idle as services might still be busy with completing start-up.
-- 
-- Kernel start-up required KERNEL_USEC microseconds.
-- 
-- Initial RAM disk start-up required INITRD_USEC microseconds.
-- 
-- Userspace start-up required 8643 microseconds.
Jul 05 19:09:44 skynet-test systemd[1]: Started User Manager for UID 1000.
-- Subject: Unit user@1000.service has finished start-up
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
-- 
-- Unit user@1000.service has finished starting up.
-- 
-- The start-up result is done.