install r-cran-devtools when using the PPA.

tasks/r-packages-install.yml

@@ -44,6 +44,14 @@
     register: install_devtools_result
     failed_when: "install_devtools_result.rc != 0 or 'had non-zero exit status' in install_devtools_result.stderr"
     changed_when: "'Added' in install_devtools_result.stdout"
+    when: not r_install_cran_repo
+
+  - name: Install the r-cran-devtools deb package
+    apt:
+      pkg: r-cran-devtools
+      state: present
+      cache_valid_time: 3600
+    when: r_install_cran_repo
 
   - name: Install R packages from the cran sources repo or from an alternative repository, latest available version.
     command: >