Respect `$TRITON_HOME` (#7907)
The default directory for Triton is only `~/.triton` if `$TRITON_HOME`
is not set or empty.
Although `TRITON_CACHE_DIR` is already supported (which deviates from
`~/.triton/cache` as used by Triton) users might expect that the root
dir variable is also supported to avoid having to set all `TRITON_*`
variables
Signed-off-by: Alexander Grund <alexander.grund@tu-dresden.de>
