Update gentoo test to current system profile
Update gentoo test to current system profile

Gentoo is at 17.1 now, most code was updated in [0], update the test job
accordingly.

[0] I0f2e7976845b1d3c55ffe8869eec0bc04a191252

Change-Id: I30e018e67f3637ce36b3ef6e20380453fe6b2bb9

openstack/diskimage-builder,switch-ch/diskimage-builder,switch-ch/diskimage-builder,openstack/diskimage-builder