Add a new public function nm_utils_copy_cert_as_user() to libnm. It
reads a certificate or key file on behalf of the given user and writes
it to a directory in /run/NetworkManager. It is useful for VPN plugins
that run as root and need to verify that the user owning the
connection (the one listed in the connection.permissions property) can
access the file.
(cherry picked from commit 1a52bbe7c9)
Add a new command to read the content of a file after switching to the
given user. This command can be used to enforce Unix filesystem
permissions when accessing a file on behalf of a user.
(cherry picked from commit 285457a5f8284f21387753d7f245e3f51ce29248)
Create a new 'nm-helpers' directory for all the helper programs, to
avoid having too many subdirs in the src directory.
(cherry picked from commit 3d76d12eee88b667d1a385b861c54fcdd4e490ed)
