Add guards making sure we are not being tricked with LV seg_type
Add guards making sure we are not being tricked with LV seg_type

Right now, we only support creation of non-linear LVs under some conditions that
allow us avoid trying to do too crazy things. Let's make sure these conditions
are met when a new LVMLogicalVolumeDevice object is being created.

rhinstaller/blivet,vpodzime/blivet,AdamWill/blivet,AdamWill/blivet,rvykydal/blivet,vpodzime/blivet,rvykydal/blivet,vojtechtrefny/blivet,vojtechtrefny/blivet,rhinstaller/blivet,jkonecny12/blivet,jkonecny12/blivet