find better solution than sys.exit for 502 error

[Marmingen]

Description

When we send a get req to MELOS (will be the same with UPRIGHT) and a 502 Bad Gateway error is returned, sys.exit(1) is called. The membership information is cached in our local dbs, thus this could in the short term be circumvented.

Specifically, add a try-except in melos_client.py