Doc: update user guide due to add new test cases and features

Doc: update user guide due to add new test cases and features

There has been added some new test cases and features, so user guide should be
updated according to the latest dovetail version.
- Add introduction about https (with cacert and without cacert)
- Add introduction about adding hosts' info
- Add introduction about downloading cirros images
- Add introduction about special configurations for running defcore and
  tempest test cases
- Add introduction about how to check defcore and tempest failed test cases

JIRA: DOVETAIL-493

Change-Id: I13aca4ee433056bd21590743a412d5d95f45fec4
Signed-off-by: xudan <xudan16@huawei.com>