By Tim Hepher and Alexander Cornwell DOHA (Reuters) -Global airlines battered by COVID-19 seem confident of narrowing their losses but still face challenges such as labour shortages at airports which could restrict post-crisis growth, industry executives at a summit in Doha said. Recent flight delays and cancellations have been widely blamed on a lack of staff as an increasing number of people desert low-paid airport work for flexible working practices that prospered during the pandemic. The head of host airline Qatar Airways, Akbar Al Baker, said labour shortages will be a big challenge in th…