recipetool: create: reimplement fetching with normal fetch/unpack tasks

recipetool: create: reimplement fetching with normal fetch/unpack tasks

Now that we have the ability to run the tasks in a more standard context
through tinfoil, change recipetool's fetching code to use that to fetch
files using it. This has the major advantage that any dependencies of
do_fetch and do_unpack (e.g. for subversion or npm) will be handled
automatically. This also has the beneficial side-effect of fixing a
recent regression that prevented this fetch operation from working with
memory resident bitbake.

Also fix devtool's usage of fetch_uri() at the same time so that we can
completely replace it.

Fixes [YOCTO #11710].

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>