Fix issue with display of VMware snapshot alert

When using the "VMWare Snapshot" functionality in the legacy webUI, if there is a failure when generating a VM snapshot, the `autosnap.py` script encodes and writes some failure information to the '/var/tmp/.vmwaresnap_fails' file.

The middleware alert plugin 'vmware_snapshot.py' reads the file on disk and updates the alert system appropriately. It's not rendered correctly in the webUI.

The message that's generated in the webUI is below:
 

WARNING: Oct. 18, 2019, 10:36 p.m. - Active Controller - Creating VMWare snapshot tank/lun00-esxi-datastore-production@auto-20191018.2230-2d of VM gl-db-c01a:
(vim.fault.ApplicationQuiesceFault) { dynamicType = , dynamicProperty = (vmodl.DynamicProperty) [], msg = "An error occurred while quiescing the virtual machine. See the virtual machine's event log for details.", faultCause = , faultMessage = (vmodl.LocalizableMessage) [ (vmodl.LocalizableMessage) { dynamicType = , dynamicProperty = (vmodl.DynamicProperty) [], key = 'msg.checkpoint.save.fail2.std3', arg = (vmodl.KeyAnyValue) [ (vmodl.KeyAnyValue) { dynamicType = , dynamicProperty = (vmodl.DynamicProperty) [], key = '1', value = 'msg.snapshot.error-QUIESCINGERROR' } ], message = 'An error occurred while saving the snapshot: Failed to quiesce the virtual machine.' }, (vmodl.LocalizableMessage) { dynamicType = , dynamicProperty = (vmodl.DynamicProperty) [], key = 'msg.snapshot.vigor.take.error', arg = (vmodl.KeyAnyValue) [ (vmodl.KeyAnyValue) { dynamicType = , dynamicProperty = (vmodl.DynamicProperty) [], key = '1', value = 'msg.snapshot.error-QUIESCINGERROR' } ], message = 'An error occurred while taking a snapshot: Failed to quiesce the virtual machine.' } ] }, gl-db-c02b: (vim.fault.ApplicationQuiesceFault) { dynamicType = , dynamicProperty = (vmodl.DynamicProperty) [], msg = "An error occurred while quiescing the virtual machine. See the virtual machine's event log for details.", faultCause = , faultMessage = (vmodl.LocalizableMessage) [ (vmodl.LocalizableMessage) { dynamicType = , dynamicProperty = (vmodl.DynamicProperty) [], key = 'msg.checkpoint.save.fail2.std3', arg = (vmodl.KeyAnyValue) [ (vmodl.KeyAnyValue) { dynamicType = , dynamicProperty = (vmodl.DynamicProperty) [], key = '1', value = 'msg.snapshot.error-QUIESCINGERROR' } ], message = 'An error occurred while saving the snapshot: Failed to quiesce the virtual machine.' }, (vmodl.LocalizableMessage) { dynamicType = , dynamicProperty = (vmodl.DynamicProperty) [], key = 'msg.snapshot.vigor.take.error', arg = (vmodl.KeyAnyValue) [ (vmodl.KeyAnyValue) { dynamicType = , dynamicProperty = (vmodl.DynamicProperty) [], key = '1', value = 'msg.snapshot.error-QUIESCINGERROR' } ], message = 'An error occurred while taking a snapshot: Failed to quiesce the virtual machine.' } ] } failed