Add option to skip generating fsid

If using another method to generate a consistent fsid, then we can
skip creation of an (unused) cluster UUID file. If cephx is disabled
as well, we can skip creation of the fetch directory entirely.

group_vars/all.sample

@@ -144,7 +144,15 @@ dummy:
 
 ## Ceph options
 #
+# Each cluster requires a unique, consistent filesystem ID. By
+# default, the playbook generates one for you and stores it in a file
+# in `fetch_directory`. If you want to customize how the fsid is
+# generated, you may find it useful to disable fsid generation to
+# avoid cluttering up your ansible repo. If you set `generate_fsid` to
+# false, you *must* generate `fsid` in another way.
 #fsid: "{{ cluster_uuid.stdout }}"
+#generate_fsid: true
+
 #cephx: true
 #cephx_require_signatures: true # Kernel RBD does NOT support signatures!
 #cephx_cluster_require_signatures: true

roles/ceph-common/defaults/main.yml

@@ -146,7 +146,15 @@ ceph_dev_redhat_distro: centos7
 
 ## Ceph options
 #
+# Each cluster requires a unique, consistent filesystem ID. By
+# default, the playbook generates one for you and stores it in a file
+# in `fetch_directory`. If you want to customize how the fsid is
+# generated, you may find it useful to disable fsid generation to
+# avoid cluttering up your ansible repo. If you set `generate_fsid` to
+# false, you *must* generate `fsid` in another way.
 fsid: "{{ cluster_uuid.stdout }}"
+generate_fsid: true
+
 cephx: true
 cephx_require_signatures: true # Kernel RBD does NOT support signatures for Kernels < 3.18!
 cephx_cluster_require_signatures: true

roles/ceph-common/tasks/main.yml

@@ -124,12 +124,16 @@
   changed_when: false
   become: false
   run_once: true
+  when:
+    cephx or
+    generate_fsid
 
 - name: generate cluster uuid
   local_action: shell python -c 'import uuid; print str(uuid.uuid4())' | tee {{ fetch_directory }}/ceph_cluster_uuid.conf
     creates="{{ fetch_directory }}/ceph_cluster_uuid.conf"
   register: cluster_uuid
   become: false
+  when: generate_fsid
 
 - name: read cluster uuid if it already exists
   local_action: command cat {{ fetch_directory }}/ceph_cluster_uuid.conf
@@ -137,6 +141,7 @@
   changed_when: false
   register: cluster_uuid
   become: false
+  when: generate_fsid
 
 - name: create ceph conf directory
   file: