Added installation of 'iperf' package to the offline images and pods

Added installation of 'iperf' package to the offline images due to
the fix in mos-spt (https://gerrit.mcp.mirantis.com/c/mcp/mos-spt/+/138830):
using iperf (v2) tool for the multiple threads test cases.

Related-PROD: PROD-36943
Change-Id: I157da5f37678b54cacdcdb38b3ea45aba347bd0a
3 files changed