Move the definitions to a separate file, thus making the lib/BUCK file
smaller.
Add a VERSION definition for powermock and reuse it for all the libary
declarations, rather than hard-coding the same version string every
time.
Depends-On: I695efcfabe67416104b0efb71f090a5303393702
Change-Id: I8840ef29d9ddfa241740fb0e4c4715c52ff07e30
