(PUP-3277) Set selinux context for new acceptance test environments

The acceptance environment_utils currently backup existing $confdir
files and copy in test environment files created in /tmp.  These test
files may have a different selinux context than $confdir, which can
result in agent -t runs coming back with selinux context changes and an
unexpected exit code of 2. Rather than just assume that all agent runs
may have resource changes, the helper instead sets $confdir's context
for the test files once they have been copied in (if selinux is
enabled).