Make mdadm a soft requirement

No point in requiring it for deployments that don't use software RAID.

Change-Id: I8b40f02cc81d3154f98fa3f2cbb4d3c7319291b8
(cherry picked from commit ab8dee0386)

ironic_python_agent/hardware.py

@@ -282,6 +282,10 @@ def is_md_device(raid_device):
         utils.execute('mdadm', '--detail', raid_device)
         LOG.debug("%s is an md device", raid_device)
         return True
+    except FileNotFoundError:
+        LOG.debug('mdadm has not been found, assuming %s is not an md device',
+                  raid_device)
+        return False
     except processutils.ProcessExecutionError:
         LOG.debug("%s is not an md device", raid_device)
         return False
@@ -333,6 +337,9 @@ def _md_scan_and_assemble():
     """
     try:
         utils.execute('mdadm', '--assemble', '--scan', '--verbose')
+    except FileNotFoundError:
+        LOG.warning('mdadm has not been found, RAID devices will not be '
+                    'supported')
     except processutils.ProcessExecutionError:
         LOG.info('No new RAID devices assembled during start-up')
 

releasenotes/notes/mdadm-d5b8c186182620b1.yaml

@@ -0,0 +1,5 @@
+---
+fixes:
+  - |
+    The ``mdadm`` utility is no longer a hard requirement. It's still required
+    if software RAID is used (even when not managed by ironic).