Add Mongo DB index in test cases with job/branch/date/status for trends
Add Mongo DB index in test cases with job/branch/date/status for trends

Add an index for the job/branch/date/status values in test case
entries which is used typically for creating graphs with pass/fail
trends over results sorted by date.  Without this index, the following
error could be seen:

    OperationFailure: Sort operation used more than the maximum
    33554432 bytes of RAM. Add an index, or specify a smaller limit.

Signed-off-by: Guillaume Tucker <e7e20b7c30f19d4ca6b81319ef81bf200369d137@collabora.com>

kernelci/kernelci-backend,kernelci/kernelci-backend