As country music’s most unlikely, and likable, newly minted star, the only real danger Aaron Watson is likely to face on the road ahead is letting his biography overshadow his material. Luckily for him, both sides of the ledger are pretty compelling: Once rejected by Nashville for his lack of “commercial appeal,” as he told Tuesday’s RodeoHouston crowd in his debut on the revolving stage, Watson retreated to his native Texas, where he played gig after gig until 2015’s The Underdog became the first independe