bitbake: cache/codeparser: Switch to a new BB_CACHEDIR variable for cache location

Currently the codeparser cache is set from CACHE, which is typically in
bitbake.conf which means we can't read/write any cache until it is found/read.
We may well have python expressions to parse before that happens.
The net result is suboptimal functioning of the codeparser cache since it will
often be invalidated by data that is never written.

This patch changes the codeparser and filechecksum caches to use BB_CACHE as
their setting and defaults it to ${TOPDIR}/cache.

The patch doesn't change where the "persistent" data such as prserver and
hash-equiavalance resides (PERSISTENT_DIR) or where the metadata parsing
cache resists (still currently CACHE). I've left those for a later patch.

The patch does ensure data parsed by the core datastore parsing calls is
written back since this is now much more useful after this change.

(Bitbake rev: ee89ade5b5a4cf9c53f336d8b800e06fbe436628)

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

bitbake/lib/bb/cache.py

@@ -838,11 +838,10 @@ class MultiProcessCache(object):
         self.cachedata = self.create_cachedata()
         self.cachedata_extras = self.create_cachedata()
 
-    def init_cache(self, d, cache_file_name=None):
-        cachedir = (d.getVar("PERSISTENT_DIR") or
-                    d.getVar("CACHE"))
-        if cachedir in [None, '']:
+    def init_cache(self, cachedir, cache_file_name=None):
+        if not cachedir:
             return
+
         bb.utils.mkdirhier(cachedir)
         self.cachefile = os.path.join(cachedir,
                                       cache_file_name or self.__class__.cache_file_name)