Added rate_interval variable into two dashboards

- updated nova/hypervisor
- updated linux/system disk i/o

Change-Id: Iaa069071ae336713c335bb1c49cca600a8c249a0
Related-Bug: PROD-30388
Related-Bug: PROD-30387
(cherry picked from commit 86dbb214ba3cd0c84292ce8c9089eb9c94c23919)
2 files changed