[vdsm] merge rights on master branch

[Dan Kenigsberg]

Nir Soffer has been contributing to Vdsm for more than two years now.
Beyond his storage-related expertise, he is well-known for his thorough
code reviews and his pains when the master branch is broken. It's time
for him to take even bigger responsibility.

David, please grant Nir Soffer with merge rights on the master branch of
Vdsm.

I'll keep merging network, virt, and infra patches myself, but much less
than before. Adam keeps his merge right as before (he tends to use them
on emergencies only).

Regards,
Dan.