Remove errant newline from generated policy file.

When running the post_process_mac_perms script
an unneeded newline is appended to modified
mac_permissions.xml file. Use sys.stdout.write
instead which avoids any formatting when printing.

Change-Id: Ib662dab1566299467371389dc236619aec40f5ac
Signed-off-by: rpcraig <rpcraig@tycho.ncsc.mil>