For short single commands, prefer a one-liner `for` with the zsh syntax:
```
for x (foo bar) print ${x}
```
Otherwise just place `; do` on the same line as the POSIX `for ... in`:
```
for x in foo bar; do
print ${x}
done
```
Closes#268
* moves check for yaourt into the other zpacman_frontend checks
* remove hardcoded sudo vs non-sudo; uses zpacman_frontend[_priv]
instead.
* these vars are set in the zpacman_frontend value sanity check.
* for values != yaourt, prepend sudo for zpacman_frontend_priv
