Flag regression after refactor

Both `fleetctl list-machines` and `fleetctl list-units` support a `-l` flag in the latest release. For example:

```
$ fleetctl list-machines -h
NAME:
   fleetctl list-machines - Enumerate the current hosts in the cluster

DESCRIPTION:
   Lists all active machines within the cluster. Previously active machines will
not appear in this list.

For easily parsable output, you can remove the column headers:
fleetctl list-machines --no-legend

Output the list without truncation:
fleetctl list-machines --full

OPTIONS:
   --full, -l	Do not ellipsize fields on output
   --no-legend	Do not print a legend (column headers)
```

However, in master, this `-l` flag is missing:

```
$ ./bin/fleetctl list-machines -h
Usage:
  -full=false: Do not ellipsize fields on output
  -no-legend=false: Do not print a legend (column headers)
flag: help requested
$ ./bin/fleetctl list-machines -l
flag provided but not defined: -l
```

The flag seems to have been dropped in commit 341433a62296e97b96d9e4f54400c54b29afafbb.