Hi there,
You have probably missed the CentOS 7 announcement (cf. Baobab migration from CentOS6 to CentOS7 ), you have to connect to baobab2.hpc.unige.ch instead.
FYI, the RSA fingerprint fro the remote SSH server is:
2048 SHA256:tKqp4nljL+EGVKl8T0VF2nS36DkHVFMpLxQOPg/gKvg no comment (RSA)
Thx, bye,
Luca