Added missing measurements and corrected errors in doc

1. Added the missing hardware snmp metrics.
2. Added a note about some compute metrics which are generated by
rate_of_change transformer on certain hypervisor.

Change-Id: I2156466e8ca5c5ec8bc808e3fbe275b591721f8a
Closes-Bug: #1393328
Merge "Added missing measurements and corrected errors in doc"