Swap conditions in the boilerplate generator so that skipping works

Otherwise the rest of the file is skipped once BpG-skip appears.
Add the bd_lvm_pvinfo function and all it needs

The bd_lvm_pvinfo function needs to return data about a given PV device. Since
we want to support GObject introspection, there are three choices:
1) an opaque structure with accessor methods for every item
2) a GObject-inherited class with all the boileplate code it needs
3) a bare C struct boxed as a minimalistic GType

Number 3 requires least code to be written and provides nice functionality and
syntax for both C and non-C code using it. The only requirements are the
function for freeing the struct and the function for creating a copy so that the
introspection layers in non-C languages know how to duplicate and delete such
structs.
Change pesize to pe_size in function's prototype

This is how the real argument is called.

Also add blank line to group related functions together.
Add the bd_lvm_vgcreate function
Add bd_lvm_vgremove/vgactivate/vgdeactivate functions