Move responsibility of querying availble disks to middleware, this
is much faster than invoking python for each disk, where GEOM tree
gets populated to XML objects, etc upon initalization.

This change also makes it much easier to distinguish between used
disks and unused disks because we have information available from
Volume object (#3685).

Ticket: #3685
Handle file names with spaces correctly
Unmount any nullfs mounts when upgrading a plugin
Import logging module
-f is not a valid flag for mount_nullfs
Sketch for the modular alert system
Implement an interface to gather alerts from external modules

Ticket:	#3855
Add alert module for HTTP SSL certificate
Alert module to check for HTTPD bind address
Alert module for iSCSI portal IP bind
Alert module for for multipath status
Alert module for volume status
Do not raise exception but log as error
Use new alert framework to show entries
Send email for critical alerts
Change tools.alert to use the new alert module
Do not limit alert in a time range
Catch up alert detail view with new API
Quote filename in Content-Disposition header field (config backup)
Remove duplicate AddVolumeIcon entry.