installserver: split DHCP part out into own role

Split the DHCP server part out of the old generic installserver role
that did everything into a separate role.

Apply that role on carbon (so it's a no-op there).

no-op (except role name) on carbon, does not touch install1001 or 2001

Bug: T132757
Change-Id: Iab414bb3b17836b535912d47feeb9409af494193