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/bzr.py

@@ -41,8 +41,9 @@ class Bzr(FetchMethod):
         init bzr specific variable within url data
         """
         # Create paths to bzr checkouts
+        bzrdir = d.getVar("BZRDIR") or (d.getVar("DL_DIR") + "/bzr")
         relpath = self._strip_leading_slashes(ud.path)
-        ud.pkgdir = os.path.join(d.expand('${BZRDIR}'), ud.host, relpath)
+        ud.pkgdir = os.path.join(bzrdir, ud.host, relpath)
 
         ud.setup_revisions(d)
 
@@ -57,7 +58,7 @@ class Bzr(FetchMethod):
         command is "fetch", "update", "revno"
         """
 
-        basecmd = d.expand('${FETCHCMD_bzr}')
+        basecmd = d.getVar("FETCHCMD_bzr") or "/usr/bin/env bzr"
 
         proto =  ud.parm.get('protocol', 'http')