[bug] Local transfers not working

[sarahwooders]

Describe the bug Local transfers on Skyplane are not working, even though they should fall back to the AWS CLI.

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Azure resource group and UMI name not configured correctly. Please reinit Azure with `skyplane init --reinit-azure`.
Using Skyplane version 0.3.1
Logging to: /tmp/skyplane/transfer_logs/20230502_011907-0d16be55/client.log
Will transfer objects from gcp:us-central1-a to aws:us-east-1
  VMs to provision: 1x aws:us-east-1, 1x gcp:us-central1-a
  Estimated egress cost: $0.12/GB
  /home/ubuntu/workspace/experiments/datasets/azure/azure_100/keys.json => s3://066278b49515470d93fc8f990d0a3d52/keys.json (7.02KB)
Continue? [Y/n]: Y
Transfer starting (Tip: Enable auto-confirmation with `skyplane config set autoconfirm true`)
01:19:11 [ERROR] Error running <lambda>: Cannot import googleapiclient.errors. Install skyplane with gcp support: `pip install
'skyplane'`
Uncaught exception: (ImportError) Cannot import googleapiclient.errors. Install skyplane with gcp support: `pip install 'skyplane'`
Please check the log file for more information, and ensure to include it if reporting an issue on Github.

To Reproduce Run a local->S3 transfer:

skyplane cp -r azure_100/ s3://066278b49515470d93fc8f990d0a3d52/

This will produce the above error.

Run a S3->local transfer:

skyplane cp s3://066278b49515470d93fc8f990d0a3d52/c5e49338a46a4391892c97fb6aa26528 .

This will silently fail.

Environment info (please complete the following information):

• OS: Linux
  • Python version: 3.7
  • Skyplane version: 0.3. 1

Additional context This error is likely due to bugs in the POSIXInterface.