Add script to adjust modules afer dep got migrated

the camptocamp/systemd module is now voxpupuli/systemd. I wrote a script
to update the namespace in .fixtures.yml, the namespace and upper
version in metadata.json and to create a pull request afterwards.

Call it like this:
```
export GITHUB_TOKEN=...
./bin/clean-git-checkouts
./bin/systemd_module_migration.sh
```

This script can be adjusted for other modules. None of our modules
install the systemd module in spec/spec_helper_acceptance.rb nor
spec/acceptance/*, so I didn't implement this.

Author: bastelfreak

bin/systemd_module_migration.sh

@@ -0,0 +1,31 @@
+#!/bin/sh
+
+if ! which hub > /dev/null ; then
+  echo "We require hub later on for the PR" >&2
+  exit 1
+fi
+
+# fix all modules with systemd in .fixtures.yml
+sed -i 's#camptocamp/puppet-systemd#voxpupuli/puppet-systemd#' modules/voxpupuli/puppet-*/.fixtures.yml
+
+# identify all modules with systemd from camptocamp in their metadata.json
+while read -r file; do
+  sed -i 's#camptocamp[-,/]systemd#puppet/systemd#' "${file}"
+done < <(grep -l "camptocamp[-,/]systemd" modules/voxpupuli/puppet-*/metadata.json)
+
+# bump the metadata because there was a recent major release
+./bin/bump-dependency-upper-bound puppet/systemd 4.0.0 modules/voxpupuli/puppet-*/metadata.json
+
+# commit and create a PR
+for module in modules/voxpupuli/puppet-* ; do
+  (cd "$module"
+  git diff --exit-code .fixtures.yml metadata.json
+  if [ $? != 0 ] ; then
+    git checkout -b systemd_voxpupuli origin/master
+    git commit -am 'switch from camptocamp/systemd to voxpupuli/systemd'
+    git push --set-upstream origin HEAD
+    # export GITHUB_TOKEN=... https://hub.github.com/hub.1.html
+    hub pull-request -m 'switch from camptocamp/systemd to voxpupuli/systemd'
+  fi
+  )
+done