Audit zygote create/write access to system_data_file.

Report any attempts by zygote to create/write files in system_data_file
so that we can ultimately move any such cases to their own type
and reduce this to read-only access.

Change-Id: I310b8da5ba5b462ef2cfdaab289628498f4d2cec
Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>