Uninformative output when specified format is not available

[denvolj]

The problem

When trying to format partitions using blivet library, you can get uninformative output like:

ansible.errors.AnsibleTaskError: Task failed: Module failed: resource to create this format mdmember is unavailable

that tells nothing about reasons "why" it's not available. After further debugging inside module I got the reason:

libblockdev plugin mdraid is loaded but some required technologies are not available (The 'mdadm' utility is not available)

but it took a lot of time.

Expected behaviour

When trying to format partition when feature not available raise an exception with more details

[denvolj]

For now I see only dirtyhack: wrap the call and take private data from library.

storage/library/blivet.py

Lines 2557 to 2560 in 547bb71

	b = Blivet()
	b.reset()
	fstab = FSTab(b)
	actions = list()

    b = Blivet()
    b.reset()

    override_format_device = b.format_device
    def format_device(device, fmt):
        if not fmt.formattable:
            raise BlivetAnsibleError("Specified format {} is unavaliable. Reason: {}".format(fmt.type, repr(fmt._plugin._availability_errors)))
        override_format_device(device, fmt)

    b.format_device = format_device
    
    fstab = FSTab(b) 
    actions = list() 

Related issue in blivet: storaged-project/blivet#1459