x86_64: Make the test environment more customizable

- Collect all test related targets under the test- prefix.

- Add target to run test suite against a `make run` instance. The
  intended use-case is that you are testing out a new build with `make
  run`, and then realize that you want to run some tests.  With this
  change, it is now possible to run `make infix-run-check` from a
  separate terminal - which attaches to the running instance and runs
  the tests.

- Provide -sh targets to spawn interactive environments, which is
  useful during debugging.

- Allow the user to supply a custom suite or list of tests to be run
  by 9PM.

.github/workflows/build.yml

@@ -61,7 +61,7 @@ jobs:
       - name: Test
         if: matrix.platform == 'x86_64' && matrix.variant == 'netconf'
         run: |
-          make infix-check
+          make test-qeneth
       - name: Prepare Artifact
         run: |
           cd output

.github/workflows/regression.yml

@@ -41,4 +41,4 @@ jobs:
           make
       - name: Regression Test
         run: |
-          make infix-check
+          make test-qeneth