Add smoke test for tmt

Cherry-picked from a122e5c6

plans.fmf

@@ -0,0 +1,4 @@
+discover:
+    how: fmf
+execute:
+    how: tmt

tests/smoke.fmf

@@ -0,0 +1,2 @@
+test: bash ./smoke.sh
+framework: shell

tests/smoke.sh

@@ -0,0 +1,12 @@
+#!/bin/bash
+set -ex
+
+username="test_$$"
+id "$username" && userdel -rf "$username"
+
+useradd "$username"
+su -l -c "echo simple-manylinux-demo > requirements.txt" "$username"
+su -l -c "micropipenv install -- --user" "$username"
+su -l -c "python3 -c 'from dummyextension.extension import hello; assert hello() == \"Hello from Python extension!\"'" "$username"
+
+userdel -rf "$username"