Make EC profiles immutable

Changing an existing EC profile can have some nasty side effects
including crashing OSD's (which is why its guarded with a --force).

Update the ceph helper to log a warning and return if an EC profile
already exists, effectively making them immutable and avoiding
any related issues.

Reconfiguration of a pool would be undertaking using actions:

  - create new EC profile
  - create new pool using new EC profile
  - copy data from old pool to new pool
  - rename old pool
  - rename new pool to original pool name

this obviously requires an outage in the consuming application.

Change-Id: I630f6b6c5e3c6dd252a85cd373d7e204b9e77245
Closes-Bug: 1897517

charmhelpers/contrib/storage/linux/ceph.py

@@ -1074,7 +1074,10 @@ def create_erasure_profile(service, profile_name,
                            erasure_plugin_technique=None):
     """Create a new erasure code profile if one does not already exist for it.
 
-    Updates the profile if it exists. Please refer to [0] for more details.
+    Profiles are considered immutable so will not be updated if the named
+    profile already exists.
+
+    Please refer to [0] for more details.
 
     0: http://docs.ceph.com/docs/master/rados/operations/erasure-code-profile/
 
@@ -1110,6 +1113,11 @@ def create_erasure_profile(service, profile_name,
     :type erasure_plugin_technique: str
     :return: None.  Can raise CalledProcessError, ValueError or AssertionError
     """
+    if erasure_profile_exists(service, profile_name):
+        log('EC profile {} exists, skipping update'.format(profile_name),
+            level=WARNING)
+        return
+
     plugin_techniques = {
         'jerasure': [
             'reed_sol_van',
@@ -1209,9 +1217,6 @@ def create_erasure_profile(service, profile_name,
         if scalar_mds:
             cmd.append('scalar-mds={}'.format(scalar_mds))
 
-    if erasure_profile_exists(service, profile_name):
-        cmd.append('--force')
-
     check_call(cmd)