Gitlab sage, Docker: Add snmp and rsync

Gitlab sage, Docker: Add snmp and rsync

Add snmp and rsync to the normal docker image. While these tools are
only required for the lab on sage, I think it's a small enough addition
to be worth always including at this point. A higher level TODO I think
may be to see if we can / should split the resulting container up, or
if there's host tooling we can remove at a later step, after building
all the software we require.

Signed-off-by: Tom Rini <trini@konsulko.com>