Adding sepolicy sign params to sign_target_files_apks.

Bug: b/217570541
Test: sign_target_files_apks --sepolicy_key=build/make/tools/releasetools/testdata/testkey_RSA4096.key
--sepolicy_cert=build/make/tools/releasetools/testdata/testkey.x509.pem target_files.zip target_out.zip
Change-Id: I4ae9f2a3297d10de68c6444dea1cd9996ad9dd11

Change-Id: I4a1ac7009ae0d6bb53c74bd34f8c74f12ea0a3b8
diff --git a/tools/releasetools/common.py b/tools/releasetools/common.py
index c2c6df1..bd3af68 100644
--- a/tools/releasetools/common.py
+++ b/tools/releasetools/common.py
@@ -97,6 +97,7 @@
     self.stash_threshold = 0.8
     self.logfile = None
     self.host_tools = {}
+    self.sepolicy_name = 'sepolicy.apex'
 
 
 OPTIONS = Options()