templates: actually create DOWNLOAD_TEMP directory

templates: actually create DOWNLOAD_TEMP directory

The way 'mktemp' is currently used you will get a temp directory in
$TMPDIR or '/tmp' and DOWNLOAD_TEMP will not be pointing to an actual
directory. This will result in the wget operations failing and the
container will fail to create:

    ERROR: Failed to download http://....

Instead we want to use the '-p' option for mktemp to set the base path
and this will ensure that the temp directory is created in the correct
location and DOWNLOAD_TEMP will be consistent with this location.

Signed-off-by: Mark Asselstine <mark.asselstine@windriver.com>