fix(application): allow both placement and constraints together.

[hmlanigan]

Description

Some constraints and placement details can conflict with each other but not all. Specifying memory size and to use a specific machine doesn't work. Spaces and placement can coexist however.

Let the jujud decide how to resolve conflicts between placement and constraints.

Fixes: #476

Type of change

• Bug fix (non-breaking change which fixes an issue)

Environment

• Juju controller version: any

• Terraform version: any

QA steps

Setup your juju environment as follows:

$ juju add-model machine-placement-constraints
Added 'machine-placement-constraints' model on localhost/localhost with credential 'localhost' for user 'admin'
$ juju add-machine
created machine 0

Run terraform init && terraform plan && terraform apply -auto-approve with the following plan:

provider juju {}

data "juju_model" "test-model" {
  name = "machine-placement-constraints"
}

resource "juju_machine" "ceph-mon-1" {
  model = data.juju_model.test-model.name
  placement = "lxd:0"
  constraints = "mem=10G"
}

Additional notes

https://warthogs.atlassian.net/browse/JUJU-5985

[cderici]

LGTM, qa went well 👍