boots: Handle boot_result_description in Json.
boots: Handle boot_result_description in Json.

  * Boot result might have a description about the failure. If that
    is the case, show it.

Change-Id: I6926694171ed091a52385f62211412720161617f

kernelci/kernelci-frontend,kernelci/kernelci-frontend,kernelci/kernelci-frontend,kernelci/kernelci-frontend