bitbake: fetch2: Ensure when downloading we are consistently in the same directory

This assists with build reproducuility. It also avoids errors if cwd
happens not to exist when we call into the fetcher. That situation
would be unusual but I hit it with the unit tests.

(From Poky rev: 86517af9e066c2da1d580fa66b7c7f0340f3403e)

(Bitbake rev: b886c6c15a58643e06ca5ad7a3ff1f7766e4f48c)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/fetch2/__init__.py

@@ -471,6 +471,8 @@ def try_mirrors(d, origud, mirrors, check = False):
             ud = FetchData(newuri, ld)
             ud.setup_localpath(ld)
 
+            os.chdir(ld.getVar("DL_DIR", True))
+
             if check:
                 found = ud.method.checkstatus(newuri, ud, ld)
                 if found:
@@ -965,6 +967,8 @@ class Fetch(object):
                 if premirroronly:
                     self.d.setVar("BB_NO_NETWORK", "1")
 
+                os.chdir(self.d.getVar("DL_DIR", True))
+
                 firsterr = None
                 if not localpath and ((not os.path.exists(ud.donestamp)) or m.need_update(u, ud, self.d)):
                     try:
@@ -1024,7 +1028,7 @@ class Fetch(object):
                 except:
                     # Finally, try checking uri, u, from MIRRORS
                     mirrors = mirror_from_string(self.d.getVar('MIRRORS', True))
-                    ret = try_mirrors (self.d, ud, mirrors, True)
+                    ret = try_mirrors(self.d, ud, mirrors, True)
 
             if not ret:
                 raise FetchError("URL %s doesn't work" % u, u)