BZ #1802206 - document --legacy-purge not working on EL5

Author: evgeni

README.md

@@ -207,6 +207,7 @@ By default, bootstrap.py does not delete the system's profile from the legacy pl
 **NOTES**:
 
 - The `--legacy-purge` switch requires a user account on RHN/Satellite 5 with permissions to remove the systems in question.
+- The `--legacy-purge` switch does not work on EL5 systems, as they lack the tooling to instruct the RHN/Satellite5 API to purge the old system entry.
 - The `--legacy-login` and `--legacy-password` options allow the correct RHN/Satellite 5 username/password to be provided to bootstrap.py.
 - bootstrap.py will prompt the user for the Legacy Password if not provided via CLI parameter.
 - If you wish to skip the migration of the system from RHN or Satellite 5 to Foreman, pass `--skip migration` as a CLI option.

bootstrap.py

@@ -1403,6 +1403,8 @@ def exec_service(service, command, failonerror=True):
 
     # > IF RHEL 5, not removing, and not moving to new capsule prepare the migration.
     if not options.remove and IS_EL5 and not options.new_capsule:
+        if options.legacy_purge:
+            print_warning("Purging the system from the Legacy environment is not supported on EL5.")
         prepare_rhel5_migration()
 
     if options.preserve_rhsm_proxy: