Allow parsing boolean in lists

[cipherboy]

This is tested in Vault's vault.TestPolicy_Parse:

path "test/types" {
    capabilities = ["create", "sudo"]
    allowed_parameters = {
        "map" = [{"good" = "one"}]
        "int" = [1, 2]
    }
    denied_parameters = {
        "string" = ["test"]
        "bool" = [false]
    }
}

Creating the equivalent in JSON fails because HCLv1 silently fails to parse this value:

"test/types": {
  "capabilities": ["create", "sudo"],
  "allowed_parameters": {
    "map": [{"good": "one"}],
    "int": [1, 2]
  },
  "denied_parameters": {
    "string": ["test"],
    "bool": [false]
  }
}

Resolves: #740