Commands are "ec2 credentials delete", "service delete", "endpoint delete".
Also update their unit tests and functional tests.
Partial-Bug: #1592906
Change-Id: I1a0b7160b803a523646d09d030e6f112c81c4c24
<service> argument of `endpoint create` command doesn't mean
`new endpoint service`, but an existent service that the new endpoint attached to.
Change-Id: I846fdb501bdea14499f42288186f375a3b2b5951