Adds the *_ORIG variables to the subiquity-server environment
so orig_environment will correctly replace mocked variables (e.g.,
$PATH).

Introduces a special set of binaries we will use to be run in the
system environment. This commit introduces subiquity-umockdev-wrapper,
which can be used to wrap ubuntu-drivers calls to fake hardware.

Utility to generate an environment for running programs outside of the
snap with the addition of the programs vendored in system_scripts.

Introduces a new UbuntuDriversInterface class that will wrap
all "ubuntu-drivers" calls with the subiquity-umockdev-wrapper
script.

install_drivers no-op until further work to copy system_scripts to
target is done.

Add option to pass "subiquity-fake-pci-devices" on the kernel
command line.

For server installs, we specifically pass "--gpgpu" to ubuntu-drivers
calls, but this stops broadcom-sta-dkms drivers from being
a candidate to install. It's faster to test on server, so we can
enable this flag to test installs of braodcom-sta-dkms on server
(which normally shouldn't happen).

Add option to pass "subiquity-server-force-no-gpgpu" on the kernel
command line.

Wrap the ubuntu-drivers command on subiquity-umockdev-wrapper during
install too. Works by copying the wrapper script to /target/usr/bin
so it will be found within $PATH by default.