Change virt-list-filesystems to use the core inspection API
instead of the deprecated Sys::Guestfs::Lib::get_partitions
function.

Update the following tools to use the C API for inspection:

 - virt-cat
 - virt-edit
 - virt-ls
 - virt-tar
 - virt-win-reg

None of the tools in the tools/ directory now use the deprecated
Perl inspection APIs.

This was probably not a security issue, but this change
makes the code cleaner by not opening the tmp file twice.

Also be more careful about error checking in close syscall.

This enables networking in the rescue shell.

This adds two new options: --format specifies the format of the
input disk, and --output-format specified the format of the output
disk.

Requiring the format of the output disk seems a bit strange at first:
after all, this is the disk that the virt-resize user has to create.
However it is needed because we sometimes reopen this disk, after
copying data over the first sector, and in theory a raw-format guest
could write a qcow2 header here and have it copied to the output
disk, which we would subsequently reopen.

The format parameter is taken from libvirt if available, else
the user should supply the '--format' parameter (eg. for local
disk files).

Sys::Guestfs::Lib is changed in two ways: firstly we take the format
string from libvirt and pass it to add_drive_opts.  Secondly we allow
an extra format =>  parameter to open_guest which allows the
format to be specified for disk images.

All the tools are changed to add an extra --format parameter allowing
the format to be specified for direct disk images.