Working GCP in gateway

[parasj]

A very simple PR that enables GCP support for the Gateway

To test:

$ source scripts/pack_docker.sh; skylark replicate-random aws:ap-northeast-1 gcp:us-central1-a --chunk-size-mb 8 --n-chunks 1024 --num-gateways 1 --num-outgoing-connections 64

=================================================
  ______  _             _                 _
 / _____)| |           | |               | |
( (____  | |  _  _   _ | |  _____   ____ | |  _
 \____ \ | |_/ )| | | || | (____ | / ___)| |_/ )
 _____) )|  _ ( | |_| || | / ___ || |    |  _ (
(______/ |_| \_) \__  | \_)\_____||_|    |_| \_)
                (____/
=================================================

            __exit__:24  | Cloud SSH key initialization: 6.46s
    replicate_random:118 | Instances will remain up and may result in continued cloud billing. Remember to call `skylark deprovision` to deprovision gateways.
      wait_for_ready:138 | Waiting for skylark-333700:gcp:us-central1-a:skylark-gcp-3e2f0698a55b478b9bb14208516cedf3 to be ready
      wait_for_ready:138 | Waiting for aws:ap-northeast-1:i-0e2d9e5b41994c304 to be ready
      wait_for_ready:140 | skylark-333700:gcp:us-central1-a:skylark-gcp-3e2f0698a55b478b9bb14208516cedf3 is ready
      wait_for_ready:140 | aws:ap-northeast-1:i-0e2d9e5b41994c304 is ready
            __exit__:24  | Provisioning instances and waiting to boot: 58.73s
       start_gateway:184 | Starting gateway aws:ap-northeast-1:i-0e2d9e5b41994c304: Installing docker
       start_gateway:184 | Starting gateway skylark-333700:gcp:us-central1-a:skylark-gcp-3e2f0698a55b478b9bb14208516cedf3: Installing docker
       start_gateway:208 | Starting gateway aws:ap-northeast-1:i-0e2d9e5b41994c304: Starting monitoring
       start_gateway:208 | Starting gateway skylark-333700:gcp:us-central1-a:skylark-gcp-3e2f0698a55b478b9bb14208516cedf3: Starting monitoring
       start_gateway:213 | Starting gateway skylark-333700:gcp:us-central1-a:skylark-gcp-3e2f0698a55b478b9bb14208516cedf3: Pulling docker image
       start_gateway:218 | Starting gateway skylark-333700:gcp:us-central1-a:skylark-gcp-3e2f0698a55b478b9bb14208516cedf3: Starting gateway container ghcr.io/parasj/skylark:local-4c0221b9868e0ee1adc4e9cbda577f7f
^[[C^[[C^[[       start_gateway:213 | Starting gateway aws:ap-northeast-1:i-0e2d9e5b41994c304: Pulling docker image
       start_gateway:218 | Starting gateway aws:ap-northeast-1:i-0e2d9e5b41994c304: Starting gateway container ghcr.io/parasj/skylark:local-4c0221b9868e0ee1adc4e9cbda577f7f
            __exit__:24  | Install gateway package on instances: 91.66s
    replicate_random:126 | Provisioned path aws:ap-northeast-1 -> gcp:us-central1-a
    replicate_random:128 | 	[aws:ap-northeast-1] http://13.115.242.234:8888/container/f5a3baccbe3f
    replicate_random:128 | 	[gcp:us-central1-a] http://35.206.81.151:8888/container/88ca16d2bad1
            __exit__:24  | Building chunk requests: 0.01s
 send_chunk_requests:241 | Sending 1024 chunk requests to 13.115.242.234
            __exit__:24  | Dispatch chunk requests: 2.19s
    replicate_random:141 | 8.00GByte replication job launched
    monitor_transfer:286 | Web dashboard running at http://54.92.213.136:8080
    monitor_transfer:330 | 35/1024 chunks done (0.27 / 8.00GB, 0.43Gbit/s, ETA=144s)
    monitor_transfer:330 | 285/1024 chunks done (2.23 / 8.00GB, 0.81Gbit/s, ETA=56s)

{"total_runtime_s": 23.721418, "throughput_gbits": 2.697983737734397, "monitor_status": "completed", "success": true}

[samkumar]

Looks good. Feel free to merge this.