Modify release tools to replace certs in MMAC files.

Added support to perform a string replace of specified
dev keys with release keys when using the release tool
scripts.

Change-Id: Id0e945b0d62720c41f5ca9764a00de4bcdecaab4
Signed-off-by: rpcraig <rpcraig@tycho.ncsc.mil>
diff --git a/tools/releasetools/common.py b/tools/releasetools/common.py
index 58582ba..a3217dd 100644
--- a/tools/releasetools/common.py
+++ b/tools/releasetools/common.py
@@ -954,3 +954,18 @@
     return PARTITION_TYPES[fstab[mount_point].fs_type], fstab[mount_point].device
   else:
     return None
+
+
+def ParseCertificate(data):
+  """Parse a PEM-format certificate."""
+  cert = []
+  save = False
+  for line in data.split("\n"):
+    if "--END CERTIFICATE--" in line:
+      break
+    if save:
+      cert.append(line)
+    if "--BEGIN CERTIFICATE--" in line:
+      save = True
+  cert = "".join(cert).decode('base64')
+  return cert