Produce less output from breeze when VERBOSE_COMMANDS is set (#15970)
Produce less output from breeze when VERBOSE_COMMANDS is set (#15970)

The prepare_usage command was being called and setting variables to
produce the full usage text for all commands at start up -- and while
this isn't a problem for speed, it makes the output when running with `bash
-x`/`VERBOSE_COMMANDS` a **lot** longer.

This change delays creating the usage variables and formatted versions
until they are needed.

Net result when running this command:

```
bash -c 'exec 5>breeze-trace.log; export BASH_XTRACEFD=5; VERBOSE_COMMANDS=true VERBOSE=true ./breeze -n shell -- -c "true"'
```

Before 4500 lines, 204K of "trace" logs

```
❯ wc -lc breeze-trace.log
  4528 204088 breeze-trace.log
```

After is 1/4 as much output:

```
❯ wc -lc breeze-trace-with-change.log
  1402  68167 breeze-trace-with-change.log
```
bolkedebruin/airflow,danielvdende/incubator-airflow,mistercrunch/airflow,nathanielvarona/airflow,cfei18/incubator-airflow,cfei18/incubator-airflow,sekikn/incubator-airflow,dhuang/incubator-airflow,cfei18/incubator-airflow,dhuang/incubator-airflow,sekikn/incubator-airflow,nathanielvarona/airflow,bolkedebruin/airflow,Acehaidrey/incubator-airflow,Acehaidrey/incubator-airflow,cfei18/incubator-airflow,sekikn/incubator-airflow,danielvdende/incubator-airflow,lyft/incubator-airflow,Acehaidrey/incubator-airflow,danielvdende/incubator-airflow,danielvdende/incubator-airflow,apache/airflow,apache/airflow,apache/airflow,danielvdende/incubator-airflow,apache/airflow,Acehaidrey/incubator-airflow,nathanielvarona/airflow,nathanielvarona/airflow,nathanielvarona/airflow,dhuang/incubator-airflow,lyft/incubator-airflow,nathanielvarona/airflow,apache/incubator-airflow,apache/incubator-airflow,mistercrunch/airflow,bolkedebruin/airflow,bolkedebruin/airflow,cfei18/incubator-airflow,mistercrunch/airflow,apache/incubator-airflow,lyft/incubator-airflow,cfei18/incubator-airflow,apache/airflow,dhuang/incubator-airflow,mistercrunch/airflow,apache/incubator-airflow,sekikn/incubator-airflow,apache/airflow,bolkedebruin/airflow,lyft/incubator-airflow,Acehaidrey/incubator-airflow,danielvdende/incubator-airflow,Acehaidrey/incubator-airflow