misc: Fix bash-completion when flags are used with the tsuru command
misc: Fix bash-completion when flags are used with the tsuru command

Previously an error would happen in situations similar to:

```
$ tsuru -t mytarget app <TAB>
-bash: compgen: -t: invalid option
compgen: usage: compgen [-abcdefgjksuv] [-o option] [-A action] [-G globpat] [-W wordlist]  [-F function] [-C command] [-X filterpat] [-P prefix] [-S suffix] [word]
```

Now everything should work as expected:
```
$ tsuru -t mytarget app <TAB><TAB>
build    create   deploy   grant    info     list     log      quota    remove   restart  revoke   router   routes   run      shell    start    stop     swap     unlock   update

$ tsuru -tmytarget app <TAB><TAB>
build    create   deploy   grant    info     list     log      quota    remove   restart  revoke   router   routes   run      shell    start    stop     swap     unlock   update

$ tsuru --target=mytarget app <TAB><TAB>
build    create   deploy   grant    info     list     log      quota    remove   restart  revoke   router   routes   run      shell    start    stop     swap     unlock   update

$ tsuru --target mytarget app <TAB><TAB>
build    create   deploy   grant    info     list     log      quota    remove   restart  revoke   router   routes   run      shell    start    stop     swap     unlock   update
```

tsuru/tsuru-client,tsuru/tsuru-client