Consul Connect CA: can't change provider

Hi all,

I'm getting error while trying to change Connect CA provider. Here are steps I've taken:

```
$ consul version
Consul v1.8.2
Revision ba7d9435e
```

1. enable Connect with Vault as CA provider:
```
$ consul connect ca get-config
{
"Provider": "vault",
"Config": {
"Address": "http://localhost:8200",
"IntermediateCertTTL": "8760h0m0s",
"IntermediatePKIPath": "consul-connect-intermediate",
"LeafCertTTL": "74h",
"RootPKIPath": "consul-connect-root",
"RotationPeriod": "24h",
"Token": "5a6a08b4-e54c-38ee-acf0-387dac8fxxxx"
},
"State": null,
"CreateIndex": 236021312,
"ModifyIndex": 251656879
}
```
2. Try to change provider to `consul`:

- Config to load (taken from working dev environment)
```
$ cat connect_consul_ca.json
{
"Provider": "consul",
"Config": {
"IntermediateCertTTL": "8760h",
"LeafCertTTL": "72h",
"RotationPeriod": "2160h"
}
}
```
- Try to upload config
```
$ connect ca set-config -config-file=connect_consul_ca.json
Error setting CA configuration: Unexpected response code: 500 (rpc error making call: error having Vault cross-sign cert: Error making API request.

URL: PUT http://localhost:8200/v1/consul-connect-root/root/sign-self-issued
Code: 500. Errors:

* 1 error occurred:
* error signing self-issued certificate: x509: requested SignatureAlgorithm does not match private key type

)
```

I tried to disable connect (remove connect stanza and rolling restart all servers) and enable it (provider set to `consul`) again but no luck, `consul connect ca get-config` still shows Vault as CA.