improve error handling for remote term service poor responses

[kmbarton423]

Determined today that one of our FHIRServerIntegrationTests for US Core 3.1.1 profile http://hl7.org/fhir/us/core/StructureDefinition/us-core-smokingstatus fails status 400 when fhir server is configured with a remote term service provider for SNOMED.

Snippet from the FHIR server log:
Unable to expand value set with url: http://hl7.org/fhir/us/core/ValueSet/us-core-observation-smokingstatus-max and version: 3.1.1
com.ibm.fhir.term.service.exception.FHIRTermServiceException: An error occurred during the ValueSet $expand operation

Below is the request and response being exchanged with the remote server for this scenario:
(request)

{
    "resourceType": "Parameters",
    "parameter": [
        {
            "name": "valueSet",
            "resource": {
                "resourceType": "ValueSet",
                "status": "active",
                "compose": {
                    "include": [
                        {
                            "system": "http://snomed.info/sct"
                        }
                    ]
                }
            }
        }
    ]
}

(response status 500)

{
    "resourceType": "OperationOutcome",
    "issue": [
        {
            "severity": "error",
            "code": "processing",
            "diagnostics": "Failed to call access method: org.snomed.langauges.ecl.ECLException: Failed to parse ECL '(  )'"
        }
    ]
}

The diagnostics returned from SNOMED is not very meaningful in this case.
There may be situations where bad responses (status 500) from the remote term server should result in a warning versus halt.

[kmbarton423]

WITHOUT the remote terminology service enabled, the store for an Observation using the noted profile above gets status 201 with the following Operation Outcome:

{
    "resourceType": "OperationOutcome",
    "issue": [
        {
            "severity": "warning",
            "code": "incomplete",
            "details": {
                "text": "Membership check was not performed: value set 'http://hl7.org/fhir/us/core/ValueSet/us-core-observation-smokingstatus-max' is empty or could not be expanded"
            },
            "expression": [
                "Observation.value"
            ]
        }
    ]
}

[kmbarton423]

WITH the remote terminology service enabled, the store for an Observation using the noted profile above gets status 400 with the following Operation Outcome:

{
    "resourceType": "OperationOutcome",
    "id": "9-55-b7-24-5afac486-9167-49f5-bbc5-ee6a3c0fb1f3",
    "issue": [
        {
            "severity": "error",
            "code": "invariant",
            "details": {
                "text": "generated-us-core-smokingstatus-5: Constraint violation: value.as(CodeableConcept).exists() and value.as(CodeableConcept).memberOf('http://hl7.org/fhir/us/core/ValueSet/us-core-observation-smokingstatus', 'preferred') and value.as(CodeableConcept).memberOf('http://hl7.org/fhir/us/core/ValueSet/us-core-observation-smokingstatus-max', 'required')"
            },
            "expression": [
                "Observation"
            ]
        }
    ]
}

[kmbarton423]

Confirmed additional error information provided indicating a problem encountered with remote term service. See example below:

`POST https://localhost:9443/fhir-server/api/v4/ValueSet/$expand
(json body)
{
"resourceType": "ValueSet",
"id": "snomed-valueset",
"url": "http://ibm.com/fhir/ValueSet/snomed-valueset",
"version": "1",
"name": "SNOMED-CT ValueSet",
"status": "active",
"compose": {
"include": [
{
"system": "http://snomed.info/sct",
"filter": [
{
"property": "concept",
"op": "is-a",
"value" : "bogus"
}
]
}
]
}
}

(json response)
{
"resourceType": "OperationOutcome",
"id": "ac-11-0-2-adf235ca-ac0f-4245-bc4f-183137616d0f",
"issue": [
{
"severity": "error",
"code": "exception",
"details": {
"text": "A communication or processing error occurred during the remote ValueSet/$expand operation (endpoint: https://snowstorm-fhir.snomedtools.org/fhir/ValueSet/$expand)"
}
},
{
"severity": "error",
"code": "processing",
"diagnostics": "Failed to call access method: org.snomed.langauges.ecl.ECLException: Failed to parse ECL ' << bogus'"
}
]
}`