tests: migrate from STI to TMT and remove broken git submodule

plans/ci.fmf

@@ -0,0 +1,5 @@
+summary: Basic smoke test
+discover:
+    how: fmf
+execute:
+    how: tmt

tests/at

@@ -1 +0,0 @@
-Subproject commit 30cccc88a2064eb05018a09d65164a26972cd5b5

tests/initscript/main.fmf

@@ -0,0 +1,12 @@
+summary: Initscript sanity
+description: ''
+contact: Radek Biba <rbiba@redhat.com>
+component:
+  - at
+test: ./runtest.sh
+framework: beakerlib
+recommend:
+  - at
+duration: 5m
+extra-summary: /CoreOS/at/Sanity/initscript
+extra-task: /CoreOS/at/Sanity/initscript

tests/initscript/runtest.sh

@@ -27,7 +27,7 @@
 # ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 # Include rhts environment
-. /usr/share/rhts-library/rhtslib.sh
+. /usr/share/beakerlib/beakerlib.sh || exit 1
 
 PACKAGE="at"
 SERVICE="atd"

tests/tests.yml

@@ -1,13 +0,0 @@
----
-# This first play always runs on the local staging system
-- hosts: localhost
-  roles:
-  - role: standard-test-beakerlib
-    tags:
-    - classic
-    - container
-    - atomic
-    tests:
-    - initscript
-    required_packages:
-    - at       # Required to run initscript