Use 400 instead of 422 for invalid input in v3 servers core

We return 400 when input is invalid for v3 api. This patch fix
this case for servers core.

DocImpact

Change-Id: If802d4dcba6ed25f7e9cb9d568a3ffd78f0f6c68
Closes-Bug: 1251538
Merge "Use 400 instead of 422 for invalid input in v3 servers core"