Fix race conditions for attributes

[aknysh]

what

• Make attributes output a list
• Fix race conditions when processing attributes

why

• attributes input is a list, we should keep the same type for the output
• Due to TF limitations, there was a race condition when merging attributes using the calculated delimiter. The delimiter was always taken from the context even if it was provided in var.delimiter, and just for attributes, the other outputs were OK.

Using the example/complete, this was the output

(note the generated id: charlie+uat+test+fire.water.earth.air, where the delimiter for the attributes was taken from the context even if at the same time it was taken from the input for all other fields)

label2 = {
  attributes = [fire.water.earth.air]
  id = charlie+uat+test+fire.water.earth.air
  name = charlie
  namespace = cloudposse
  stage = test
}
label2_context = {
  attributes = [fire.water.earth.air]
  delimiter = [+]
  environment = [uat]
  label_order = [name environment stage attributes]
  name = [charlie]
  namespace = [cloudposse]
  stage = [test]
  tags_keys = [City Environment Name Namespace Stage]
  tags_values = [London Public charlie+uat+test+fire.water.earth.air cloudposse test]
}
label2_tags = {
  City = London
  Environment = Public
  Name = charlie+uat+test+fire.water.earth.air
  Namespace = cloudposse
  Stage = test
}

After the race condition fix:

label2 = {
  attributes = [fire water earth air]
  id = charlie+uat+test+fire+water+earth+air
  name = charlie
  namespace = cloudposse
  stage = test
}
label2_context = {
  attributes = [fire water earth air]
  delimiter = [+]
  environment = [uat]
  label_order = [name environment stage attributes]
  name = [charlie]
  namespace = [cloudposse]
  stage = [test]
  tags_keys = [City Environment Name Namespace Stage]
  tags_values = [London Public charlie+uat+test+fire+water+earth+air cloudposse test]
}
label2_tags = {
  City = London
  Environment = Public
  Name = charlie+uat+test+fire+water+earth+air
  Namespace = cloudposse
  Stage = test
}

[osterman]

Let's keep - as the recommended delimiter