[fb] Configurable tempfile.tempdir for local file upload

Branch: cdh4-2.5.0_4.5.0.x

Add new feature to set [filebrowser] tempfile.tempdir. Certain environment may restrict /tmp storage limit

This conforms the rule of tempfile implementation, see https://docs.python.org/2/library/tempfile.html
add
[filebrowser]
filebrowser_tempdir="/set/alternative/tmpdir" | note: default default behaviour filebrowser_tempdir=None

Tests:
CDH4.6/CDH4.5

Below, hue.ini confirmed that uploading a zip file, Hue placed its "tmpfilename.upload" in "/alt_tmp_dir/hue_tmpdir" (or any folder that hue has rw access)
[filebrowser]
filebrowser_tempdir="/alt_tmp_dir/hue_tmpdir"
Default behaviour is filebrowser_tempdir=None ; Hue copies its "tmpfilename.upload" in "/tmp"