IKEv2 ECDSA certificate based authentication

This tests for authby=ecdsa-sha2_384,rsa which should still use
ecdsa, as we only have ecdsa certificates.

It should not fail with:

+"westnet-eastnet-ikev2" #1: NSS: RSA DSS sign function failed: SEC_ERROR_INVALID_KEY: The key does not support the requested operation.
 "westnet-eastnet-ikev2" #1: sent IKE_AUTH request to 192.1.2.23:UDP/500
-"westnet-eastnet-ikev2" #1: initiator established IKE SA; authenticated peer certificate 'C=CH, O=strongSwan, CN=strongEast' and P-384 ECDSA with SHA2_384 digital signature issued by 'C=CH, O=strongSwan, CN=strongSwan CA'
-"westnet-eastnet-ikev2" #2: initiator established Child SA using #1; IPsec tunnel [192.0.1.0/24===192.0.2.0/24] {ESP/ESN=>0xESPESP <0xESPESP xfrm=AES_GCM_16_256-NONE DPD=passive}
+"westnet-eastnet-ikev2" #1: IKE SA authentication request rejected by peer: AUTHENTICATION_FAILED

