~/.local/share/juju:
clouds.yaml  config.yaml  credential.yaml

clouds:
  systack:
    type: openstack
    regions:
      RegionOne:
        endpoint: http://x.x.x./v2.0
        auth-types: [userpass]

credentials:
  systack:
    default-credential: xxxx
    default-region: RegionOne
    juju-dev:
      auth-type: userpass
      password: xxxx
      username: xxxx
      tenant-name: xxxx
      domain-name: default

config.yaml

agent-metadata-url: https://streams.canonical.com/juju/tools/
agent-stream: devel
default-series: centos7

ubuntu@localhost:~/.local/share/juju$ juju bootstrap openstack systack --config config.yaml --debug
00:14:10 INFO  juju.cmd supercommand.go:63 running juju [2.0-beta17 gc go1.6]
00:14:10 INFO  cmd cmd.go:141 no credentials found, checking environment
00:14:10 ERROR cmd supercommand.go:458 detecting credentials for "systack" cloud provider: openstack credentials not found
00:14:10 DEBUG cmd supercommand.go:459 (error details: [{github.com/juju/juju/cmd/juju/commands/bootstrap.go:407: } {github.com/juju/juju/cmd/modelcmd/credentials.go:122: detecting credentials for "systack" cloud provider} {github.com/juju/juju/provider/openstack/credentials.go:99: openstack credentials not found}])