tools: Check for dangling --format parameters (RHBZ#1140894).

In most C tools, virt-sysprep and virt-customize, you have to put the
--format parameter before the corresponding -a parameter.  ie.  The
following is correct:

  guestfish --format qcow2 -a disk1 -a disk2

But the following is incorrect.  The --format parameter is dangling
and prior to this commit would have been silently ignored:

  guestfish -a disk1 -a disk2 --format qcow2

After this change, dangling --format parameters now lead to an error:

  guestfish: --format parameter must appear before -a parameter

In virt-customize, also check that --attach-format parameter appears
before --attach parameter.

Thanks: Lingfei Kong