storage pool source name checking

[kokey]

If a storage pool source name does not exist, then the module stops being able to modify it.
E.g.

libvirt_pool { 'default' :
	ensure     => present,
	type       => 'logical',
	autostart  => true,
	sourcedev  => '/dev/sda5',
	sourcename => 'this_name_is_nonsense',
	target     => '/dev/vm',
}

After trying to apply that, the pool is created but not active, but also can't be updated by the module to fix it, or any other libvirt_pool created on the same device. Ideally there should be a sanity check on sourcename to name sure it exists, then it would avoid getting into this situation.

The way to work around it is to virsh pool-edit and fix the name, then pool-start, then fix the name in the declaration.

[trefzer]

I do not have time to look at this issue, if anyone, please submit a pull request !