Switching flow for assets:precompile in case of Windows

Because of the character limitation on Windows Command Line, the existing CLASSPATH assignment was failing. The commandline was exceeding 17000 characters while the limit is ~8000. Spilting the commands into multiple line and echoing the CLASSPATH value from a file rather than having it as part of the command line.
Merge pull request #541 from sachinsudheendra/jsunit-win-windows-path-length

Switching flow for assets:precompile in case of Windows