feat(hoststack): Add stat pre/post actions

feat(hoststack): Add stat pre/post actions

While adding runtime actions to hoststack tests is not easy,
adding pre and post actions for stats is easy.
The main hoststack measurement is treated as the stats trial,
the same way as the 10 measurements in MRR tests are.

+ Remove the previous partial info via "show" CLI commands.
- As in other VPP tests, stat telemetry is not exported.

Change-Id: Ib567aa810418568520d4d543c6d50431e85a3269
Signed-off-by: Vratko Polak <vrpolak@cisco.com>
(cherry picked from commit 3dc8a53fc419e0491d1bd53e23473aed019fedc1)