Bump app version number to 2015.2.1.
Bump app version number to 2015.2.1.

Change-Id: Ibccb2d70c59624a4f2876fc2f28470a153c6beba

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