CT: disable cth_readable_failonly hook when verbose option is set

[stolen]

The story:

• I got used to ct:pal as a convenient way of showing what's going on.
• at some point I noticed I cannot see my logs when running tests via rebar3 ct
• options -vvv and --verbosity 99 allowed to see ct:print, but not ct:pal
• I even employed dbg, and it showed ct:pal is not even called
• found the cth_readable_failonly stuff (parse_transform and hook)

So, I think current behaviour is harmful:

• cth_readable_failonly is unavoidable in current main, making it hard to debug tests
• there is no mention in docs about this behavior
• even making test fail (ct:fail(test) in the end) just for debugging screws things up -- ct:print and ct:pal outputs are reordered

This PR disables cth_readable_failonly hook when verbose option is given by user.
With this change rebar3 ct behaves more consistent to me:

• by default, I see no output from ct:print or ct:pal (by design, I suppose)
• with -v option I see both (as I expect)