change the naming of the info file

it was something like:
  leb-origen-precise_nano_20120425-40.img.bz2.info.txt

its now:
  leb-origen-precise_nano_20120425-40.info.txt
diff --git a/build-images.py b/build-images.py
index 61446e8..3dbd2b9 100755
--- a/build-images.py
+++ b/build-images.py
@@ -105,7 +105,7 @@
             md5.update(data)
     return md5.hexdigest()
 
-def image_info(bz2file, binary_file):
+def image_info(infofile, bz2file, binary_file):
     ''' prints out the md5sum and rfs info for the given image
     '''
     print "building image info for: %s" % bz2file
@@ -113,7 +113,7 @@
 
     binary_file = os.path.basename(binary_file)
 
-    with open('%s.info.txt' % bz2file, 'w') as f:
+    with open(infofile, 'w') as f:
         f.write("%s md5sum(%s)\n" % (os.path.basename(bz2file), md5))
         f.write("root file system: %s\n" % binary_file)
 
@@ -121,6 +121,7 @@
     print "building image: %s" % imgfile
     hwpi = HWPACKS[hwpack]
     size = BINARIES[binary]
+    infofile = '%s.info.txt' % os.path.splitext(imgfile)[0]
 
     print 'running l-m-c: %s' % lmc
     args = [lmc,
@@ -143,7 +144,7 @@
     cmd_runner.run(args, as_root=True).wait()
     bz2file = compress_image(imgfile)
     zsync_image(bz2file)
-    image_info(bz2file, binary_file)
+    image_info(infofile, bz2file, binary_file)
 
 class SnapshotCrawler:
     def __init__(self, date, platform, hwpacks, binaries):