Add support for INDEX_CLEANUP and TRUNCATE to vacuumdb

Hi hackers,

I quickly put together a patch to add INDEX_CLEANUP and TRUNCATE to
vacuumdb before noticing a previous thread for it [0].  My  take on it
was to just name the options --skip-index-cleanup and --skip-truncate.
While that does not give you a direct mapping to the corresponding
VACUUM options, it simplifies the patch by avoiding the boolean
parameter parsing stuff altogether.

Nathan

[0] https://postgr.es/m/CAHGQGwENx3Kvxq0U%2BwkGAdoAd89iaaWo_Pd5LBPUO4AqqhgyYQ%40mail.gmail.com