ruby: Add init.rb file to PTEST installation path

ruby: Add init.rb file to PTEST installation path

This patch copies the init.rb file to the tool testing directory in the
PTEST installation path during installation. This modification can address
the following errors:

BEGIN: /usr/lib64/ruby/ptest
/usr/lib64/ruby/ptest/tool/test/runner.rb:4:in `require_relative': cannot load such file -- /usr/lib64/ruby/ptest/tool/test/init (LoadError)
	from /usr/lib64/ruby/ptest/tool/test/runner.rb:4:in `<top (required)>'
	from ./test/runner.rb:5:in `require_relative'
	from ./test/runner.rb:5:in `<main>'

Signed-off-by: Jiaying Song <jiaying.song.cn@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>