Install yq needed for tmt integration tests

Also remove irrelevant `adjust` rule for `centos-7` as the `epel-7`
packit job was dropped more than a year ago.

plans/integration.fmf

@@ -6,8 +6,27 @@ discover:
     ref: fedora
     filter: 'tier: 1, 2'
 prepare:
-    how: install
-    package: tmt-all
-adjust:
-    enabled: false
-    when: distro == centos-7
+  - how: install
+    package:
+      - jq
+      - python3-pip
+      - tmt-all
+  - how: shell
+    script:
+      # Try to install into .local first, if that fails, try without --user.
+      # In the sane world, tmt would be running in a virtualenv, and we'd
+      # install yq there. Otherwise, we'd change system packages, but we'd
+      # have to run as root to do that, and who's running tmt test suite
+      # as root?
+      #
+      # We need to freeze yq to 3.1.1 so that it's installable on el8 as
+      # newer yq requires tomlkit>=0.11.7 which is python 3.7+ only.
+      - pip3 install --user yq==3.1.1 || pip3 install yq==3.1.1
+      - yq --help
+
+adjust+:
+  - when: distro == centos-stream-8 and trigger == commit
+    environment+:
+      # Default PATH, spiked with ~/.local/bin for Python packages installed with --user.
+      # This is needed on Centos Stream 8 where the user-specific path is not in PATH.
+      PATH: "/root/.local/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"