update installer under scenario

1. post, add one or more new installers
2. update, replace existed installers as a totality
3. delete, delete one or more installers by name
4. in post&update, if schema is not consistent with ScenarioInstaller model,
BadRequest will be raised(only extra keys will be detected currently)
5. in post, if installer already exist, return Conflict with already exist
message
6. in update, if a installer appears more than once, also return Conflict
with already exist message

Change-Id: I830dba3bcf5f1a9d1c93513b4aae59009f69dc8f
Signed-off-by: SerenaFeng <feng.xiaowei@zte.com.cn>