[ci] Added argotest-based integration tests

This commits adds a gitlab-ci integration test target, and the
.integration.nix file, which specifies the exact test version pinning to
use.

.gitignore

@@ -40,3 +40,6 @@ config.status
 configure
 libtool
 m4
+
+#ci
+_output

.gitlab-ci.yml

+stages:
+  - test
+
+integration.test:
+  stage: test
+  script:
+    - nix-shell .integration.nix --run "argotk.hs helloworld"
+  artifacts:
+    paths:
+      - _output/cmd_err.log
+      - _output/cmd_out.log
+      - _output/daemon_out.log
+      - _output/daemon_out.log
+      - _output/nrm.log
+      - _output/time.log
+      - _output/.argo_nodeos_config_exit_message
+    expire_in: 1 week
+  except:
+    - /^wip\/.*/
+    - /^WIP\/.*/
+  tags:
+    - integration

.integration.nix

+{ argotest ? (builtins.fetchGit {
+    url = https://xgitlab.cels.anl.gov/argo/argotest.git;
+    ref="refactor-argotk";
+    rev="e96e94a17a8046d0f7c8b2908dcb5fb25ead7b96"; })
+}:
+(import argotest {
+  containers-src = ./.;
+}).test