tools: implement --short-options

Just like --long-options, it makes it possible to know which short
options are supported by each tool; this can help improving the bash
completion, for example.
bash: execute --long-options only when needed

Delay the execution of $tool --long-options only when really using its
output.
bash: complete also short options

Propose both short and long options when trying to complete a single
dash ("-").
bash: complete some params for resize, sparsify, and builder

Hardcode the list of fixed arguments for some of the parameters of these
tools.
bash: add a completion module for virt-v2v