[LTP] [PATCH 1/3] tst_test.sh: Simplify tst_cmd_available()

[Petr Vorel]

Hi Li, all,

...
> Another reason, I guess, is `command -v ` looks to match the function name
> more:).
> But it depends on you, I'm OK with any of them.
I merged it with "command -v" and second commit.

Kind regards,
Petr