clean up old Ubuntu initrds

for some reason /boot contains both initrds with and without .img
even if the ones with are not used, however, as /boot space is limited
they prevent upgrades of packages, failing our pipelines

delete them

we don't really care about new kernels, or rebooting those VMs, but we
care about updated userland, and this prevents it

See lavabit/robox#294 for details

roles/vagrant_workarounds/tasks/main.yml

@@ -7,3 +7,9 @@
     vtype: boolean
   when:
     - ansible_os_family == 'Debian'
+
+# workaround for https://github.com/lavabit/robox/issues/294
+- name: clean up old Ubuntu initrds
+  shell: rm -f /boot/*-generic.img
+  when:
+    - ansible_os_family == 'Debian'