This updates the format of various usage strings to be more consistent
with other parts of the CLI.
- Use `[OPTIONS]` to indicate where command-specific options should be added
- Use `[SERVICE...]` to indicate zero-or-more services
- Remove some usage strings for specific options (e.g. `-e NAME=VAL`), as that
option is part of the already mentioned `[OPTIONS]` and we don't provide usage
for each possible option that can be passed.
- Remove `[--]`, which (I think) was needed for the Python implementation, but is
a general feature to stop processing flag-options.
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
