CA-142415: Distinguish rebooting from 32-bit-wrapping for perf data

Some performance statistic data (such as iops, throughput) will be
reset to zero due to the VM rebooting.  Those performance data may
also decrease if the values exceed the 32-bit limit and wrap.

For VM level counters they can be easily distinguished. While for host
level counters we have no way to exactly figure out one from another.

Based on an assumption that those performance data would not accumulate
rapidly so that we have a way to distinguish them from each other.

Signed-off-by: Kaifeng Zhu <kaifeng.zhu@citrix.com>