Validator Handler should support different base url

[BalloonWen]

e.g. in the OpenAPI spec

servers:
- url: https://${host}/{path1}/{path2}/v1

the default baseUrl in OpenAPIHelper is "/{path1}/{path2}/v1", then whenever a request comes, it will match "/{path1}/{path2}/v1", then rewrite it to "/"
but if there is already a rewrite happening in between (e.g. rewrite by ingress), this will case the normalization fail

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update
It is hard for the OpenAPIHelper to know which paths should be rewrite, thus, we should support relative server url

[stevehu]

Validator Handler should support different base url light-rest-4j master