pack_firmware: Permit ./ in front of archive member names

Older firmware archives (e.g., bcs://kevin_fw_8785.94.7.tbz2) appear
to have member names that start with "./".  No harm in allowing this.

BUG=b:216515833
TEST=kevin builds with CL:*4506133

Change-Id: I4f4c79448625fbc68552bea0a6cea862c8e4e154
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/firmware/+/3420997
Tested-by: Jack Rosenthal <jrosenth@chromium.org>
Auto-Submit: Jack Rosenthal <jrosenth@chromium.org>
Commit-Queue: Jack Rosenthal <jrosenth@chromium.org>
Reviewed-by: Jacob Rasmussen <jacobraz@google.com>
Commit-Queue: Jacob Rasmussen <jacobraz@google.com>

pack_firmware.py

diff --git a/pack_firmware.py b/pack_firmware.py
index 4a7173c..9735c81 100755
--- a/pack_firmware.py
+++ b/pack_firmware.py
@@ -669,7 +669,10 @@
       if len(members) != 1:
         raise PackError("Expected 1 member in file '%s' but found %d" %
                         (pathname, len(members)))
-      if '/' in members[0].name:
+      name = members[0].name
+      if name.startswith('./'):
+        name = name[2:]
+      if '/' in name:
         raise PackError("Tar file '%s' member '%s' should be a simple name" %
                         (pathname, members[0].name))
       tar.extractall(self._tmpdir, members)