oeqa.buildperf: store measurements as a dict (object) in the JSON report
Store measurements as a dict, instead of an array, in the JSON report.
This change makes traversing of the report much easier. The change also
disallows identically named measurements under one test, as a sanity
check for the test cases.
[YOCTO #10590]
Signed-off-by: Markus Lehtonen <markus.lehtonen@linux.intel.com> Signed-off-by: Ross Burton <ross.burton@intel.com>
