fetch: add common helper _strip_leading_slashes()

Several fetcher need a way to strip leading slashes off a local path.
This helper-function consolidates all such occurances.

(Bitbake rev: 823a02185ed109054c6c1ae366221aaed0353f24)

Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>
Signed-off-by: Richard Purdie <rpurdie@linux.intel.com>

bitbake/lib/bb/fetch/__init__.py

@@ -607,6 +607,13 @@ class Fetch(object):
         and duplicate code execution)
         """
         return url
+    def _strip_leading_slashes(self, relpath):
+        """
+        Remove leading slash as os.path.join can't cope
+        """
+        while os.path.isabs(relpath):
+            relpath = relpath[1:]
+        return relpath
 
     def setUrls(self, urls):
         self.__urls = urls