terraform_cli: support path and env and in terraform_cli blocks

At some point during the serial to multiplex rewrite of Enos we stopped
respecting the special `path` and `env` attributes in `terraform_cli`
blocks.

I discovered this when attempting to test an older version of Terraform
with enos by setting the `path` and it was still resolving the latest
version which it found via the `PATH`.

This resolves that by configuring the Terraform executor in the
workspace with any special `terraform_cli` variables that have been set
in the flight plan.

Signed-off-by: Ryan Cragun <[email protected]>

internal/server/service_v1.go

@@ -349,6 +349,7 @@ func (s *ServiceV1) dispatch(
 		flightplan.DecodeTargetAll,
 		f,
 	)
+
 	hclDiags := scenarioDecoder.DecodeAll(ctx, fp)
 	if len(hclDiags) > 0 {
 		decRes.Diagnostics = append(decRes.GetDiagnostics(), diagnostics.FromHCL(nil, hclDiags)...)
@@ -381,11 +382,21 @@ func (s *ServiceV1) dispatch(
 
 	for _, scenario := range scenarios {
 		req := &pb.Operation_Request{}
+
+		// Configure our Terraform executor with any values that are present in the "terraform_cli" block
+		if cli := scenario.TerraformCLI; cli != nil {
+			if cli.Path != "" {
+				baseReq.Workspace.TfExecCfg.BinPath = cli.Path
+			}
+			for k, v := range cli.Env {
+				baseReq.Workspace.TfExecCfg.Env[k] = v
+			}
+		}
+
 		err := proto.Copy(baseReq, req)
 		if err != nil {
 			diags = append(diags, diagnostics.FromErr(err)...)
-
-			continue
+			break
 		}
 
 		req.Scenario = scenario.Ref()