The bridge V2 HTTP API start operation should return a 400 error if the
start is unsuccessful.
The bridge V1 HTTP API compatibility layer for Bridge V2 should return a
400 error if the start or restart operation is unsuccessful.
This commit fixes the above and adds tests that checks this for the V2
HTTP API.
Fixes:
https://emqx.atlassian.net/browse/EMQX-11304