compose: Context not found when given on docker-compose CLI

Description of the issue

When using the docker-compose command line --context parameter, the context reports not found, even though it’s found when using docker commands.

Context information (for bug reports)

Output of docker-compose version

docker-compose version 1.26.0-rc4, build d279b7a8
docker-py version: 4.2.0
CPython version: 3.7.7
OpenSSL version: OpenSSL 1.1.0l  10 Sep 2019

Output of docker version

Client: Docker Engine - Community
 Version:           19.03.8
 API version:       1.40
 Go version:        go1.12.17
 Git commit:        afacb8b7f0
 Built:             Wed Mar 11 01:25:46 2020
 OS/Arch:           linux/amd64
 Experimental:      false

Server: Docker Engine - Community
 Engine:
  Version:          19.03.8
  API version:      1.40 (minimum version 1.12)
  Go version:       go1.12.17
  Git commit:       afacb8b7f0
  Built:            Wed Mar 11 01:24:19 2020
  OS/Arch:          linux/amd64
  Experimental:     false
 containerd:
  Version:          1.2.13
  GitCommit:        7ad184331fa3e55e52b890ea95e65ba581ae3429
 runc:
  Version:          1.0.0-rc10
  GitCommit:        dc9208a3303feef5b3839f4323d9beb36df0a9dd
 docker-init:
  Version:          0.18.0
  GitCommit:        fec3683

Output of docker-compose config (Make sure to add the relevant -f and other flags)

services:
  test:
    container_name: test
    image: alpine
version: '3.6'

Steps to reproduce the issue

1. Create a context (in this case with ssh):

docker context create testctx --default-stack-orchestrator swarm --docker "host=ssh://user@remote"

1. Verify context is functional:

docker --context testctx ps

1. Issue a compose command on the context (this is what fails):

docker-compose --context testctx up -d

1. Issue the same compose command except with the host parameter to verify endpoint (this works for me):

docker-compose -H ssh://user@remote up -d

Observed result

ERROR: Context 'testctx' not found

Expected result

The docker-compose should remotely execute on the context’s machine.

Stacktrace / full error message

(with --verbose)

docker.utils.config.find_config_file: Trying paths: ['/home/user/.docker/config.json', '/home/user/.dockercfg']
docker.utils.config.find_config_file: No config file found
ERROR: compose.cli.main.main: Context 'testctx' not found

Additional information

OS version / distribution, docker-compose install method, etc.

Ubuntu 18.04.

Docker installed via this ansible role, docker-compose installed via ansible task:

- name: Update docker-compose to bleeding edge # Required for docker context support
  get_url:
    url: https://github.com/docker/compose/releases/download/1.26.0-rc4/docker-compose-Linux-x86_64
    dest: /usr/local/bin/docker-compose
    checksum: sha256:3ad2031c7daae160b8987538a60261475b3e17dfccf6fb96c1ae67d23afecdb8