build: use own temp directory and preferences for gwt

during build, gwt generates a lots of files into temp directory which
not always cleaned up.

best to generate these at own project directory so once project is
cleaned up these will also be cleaned up.

to avoid conflicts with other running instances, set java preferences
location to be in temp directory as well.

Change-Id: If2551534ccf0c181fdd755c64e11328ad24b47b2
Signed-off-by: Alon Bar-Lev <alonbl@redhat.com>