[tracking] Simplify updatemanager job

- sed all the URI lines with a simple replacement
- document policy requirements

src/modules/tracking/TrackingJobs.cpp

@@ -134,17 +134,15 @@ TrackingMachineUpdateManagerJob::prettyStatusMessage() const
 Calamares::JobResult
 TrackingMachineUpdateManagerJob::exec()
 {
-    static const auto script = QStringLiteral(
-        R"x(
-MACHINE_ID=`cat /etc/machine-id`
-sed -i "s,URI =.*,URI = http://releases.neon.kde.org/meta-release/${MACHINE_ID}," /etc/update-manager/meta-release
-sed -i "s,URI_LTS =.*,URI_LTS = http://releases.neon.kde.org/meta-release-lts/${MACHINE_ID}," /etc/update-manager/meta-release
-true
-)x" );
-    int r = CalamaresUtils::System::instance()->targetEnvCall( "/bin/sh",
+    static const auto script = QStringLiteral( "sed -i '/^URI/s,${MACHINE_ID},'`cat /etc/machine-id`',' /etc/update-manager/meta-release || true" );
+
+    auto res = CalamaresUtils::System::instance()->runCommand(
+        CalamaresUtils::System::RunLocation::RunInTarget,
+        QStringList { QStringLiteral( "/bin/sh" ) },
         QString(),  // Working dir
-                                                               script,
+        script,  // standard input
         std::chrono::seconds( 1 ) );
+    int r = res.first;
 
     if ( r == 0 )
     {

src/modules/tracking/tracking.conf

@@ -34,8 +34,10 @@
 # Each area has a key *policy*, which is a Url to be opened when
 # the user clicks on the corresponding Help button for an explanation
 # of the details of that particular kind of tracking. If no policy
-# is set, the help button is hidden. The example policy links
-# go to Calamares' generic user manual.
+# is set, that tracking style is disabled. The example policy links
+# go to Calamares' generic user manual (which is a terrible idea
+# for distro's: you have GDPR obligations under most of these tracking
+# styles, so do your homework).
 #
 # Each area may have other configuration keys, depending on the
 # area and how it needs to be configured.
@@ -48,8 +50,7 @@
 ---
 # This is the global policy; it is displayed as a link on the page.
 # If blank or commented out, no link is displayed on the tracking
-# page. It is recommended to either provide policy URLs for each
-# area, *or* one general link, and not to mix them.
+# page. You **must** provide policy links per-area as well.
 policy:  "https://github.com/calamares/calamares/wiki/Use-Guide#installation-tracking"
 
 # This is the default level to enable for tracking. If commented out,
@@ -79,9 +80,14 @@ install:
 #           needs to be done. There is currently only one valid
 #           style, "updatemanager", which edits two files in the installed
 #           system to enable system-tracking.
+#
+# Per-style documentation:
+#   - updatemanager replaces the literal string "${MACHINE_ID}" with the contents of
+#     /etc/machine-id, in lines starting with "URI" in the file /etc/update-manager/meta-release
 machine:
     enabled: false
     style: updatemanager
+    policy:  "https://github.com/calamares/calamares/wiki/Use-Guide#machine-tracking"
 
 # The user area is not yet implemented, and has no specific configuration.
 user: