Collection manager not parsing errors correctly

There are a number of errors that have changed their error message response from the server and therefore the errors are not being parsed correctly here: https://github.com/couchbase/couchbase-jvm-clients/blob/44d009ffc2c3920d516a2ae1345132f4a86946b7/scala-client/src/main/scala/com/couchbase/client/scala/manager/collection/ReactiveCollectionManager.scala#L214

(Same issue as in JCBC-1728, but bug not in shared code)

Here's a list of the current (7.0.0-3507) error responses:

Scope already exists:
{"errors":{"_":"Scope with name \"2d33a596-8\" already exists"}}

Collection already exists:
{"errors":{"_":"Collection with name \"b185d9f9-0\" in scope \"7df92294-3\" already exists"}}

Scope not found:
{"errors":{"_":"Unknown error {error,{scope_not_found,\"foobar\"}}"}}

Collection not found
{"errors":{"_":"Unknown error {error,{collection_not_found,\"a9e4f276-3\",\"1141f1d0-b\"}}"}}

There are a number of test failures related to this: http://sdk.jenkins.couchbase.com/view/Nightly/job/jvm/job/jvm-clients/job/couchbase-jvm-clients-scipted-build-pipeline/533/testReport/com.couchbase.client.scala.manager/CollectionManagerSpec/