bitbake: fetch2: unify the way fetchers determine DL_DIR and FETCHCMD

Currently there is quite some variation between the fetchers in terms
of how they determine the subdirectory within DL_DIR and the base
fetch command to run. Some rely on variables being set externally
(e.g. from bitbake.conf in oe-core), some respect these external
variables but provide fallback defaults and some use only hardcoded
internal values. Try to unify the approach used across the various
fetchers.

(Bitbake rev: efd5e35af4b08501c67e8b30f30d9457f6fdf610)

Signed-off-by: Andre McCurdy <armccurdy@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/fetch2/osc.py

@@ -32,8 +32,9 @@ class Osc(FetchMethod):
         ud.module = ud.parm["module"]
 
         # Create paths to osc checkouts
+        oscdir = d.getVar("OSCDIR") or (d.getVar("DL_DIR") + "/osc")
         relpath = self._strip_leading_slashes(ud.path)
-        ud.pkgdir = os.path.join(d.getVar('OSCDIR'), ud.host)
+        ud.pkgdir = os.path.join(oscdir, ud.host)
         ud.moddir = os.path.join(ud.pkgdir, relpath, ud.module)
 
         if 'rev' in ud.parm:
@@ -54,7 +55,7 @@ class Osc(FetchMethod):
         command is "fetch", "update", "info"
         """
 
-        basecmd = d.expand('${FETCHCMD_osc}')
+        basecmd = d.getVar("FETCHCMD_osc") or "/usr/bin/env osc"
 
         proto = ud.parm.get('protocol', 'ocs')