HOUSTON — Walgreens will receive a jolt to its brand image in February as the chain begins playing host to NRG’s eVgo electric vehicle charging stations across 18 locations in the Hous­ton market. The eye-catching stations will help position Walgreens, and such other participating retailers as H-E-B and Best Buy, as cutting-edge companies with an eye to the future — and as responsible neighbors intent to make good on the promise of sustainability.