shell: add option to disable pcspkr blacklisting

Unfortunately, there is a popular hoster that offers systems where
blacklisting pcspkr results in a failure. Since these are virtual
systems its not really relevant anyway. The simplest solution was to
make it configurable.

shell/defaults/main.yml

@@ -8,3 +8,5 @@ shell_software:
   - pwgen
   - snmp
   - telnet
+
+shell_blacklist_pcspkr: true

shell/tasks/shell.yml

@@ -129,7 +129,7 @@
 - name: ensure that pcspeaker remains silent
   kernel_blacklist:
     name: pcspkr
-    state: present
+    state: "{{ 'present' if shell_blacklist_pcspkr else 'absent' }}"
   notify:
     - rerun depmod
     - update initramfs