[FEATURE] Add ability to specify each node's user name, password, and hosts if known

[davidallendj]

Description of Issue

There are some situations where it is possible to have a cluster with different BMC login information. In these situations, it would be necessary to be able to specify each individual node's login information opposed to only using to the one specified currently.

Possible Solutions

There are at least three approaches to consider here. We can specify the BMC login information via:

1. the YAML config file
2. environment variables
3. CLI flags

In the config file, the format may look something like this:

...
collect:
  login:
    - host: 172.16.0.101
      username: "username1"
      password: "password1"
    - host: 172.16.0.102
      username: "username2"
      password: "password2"
    # alternatively...
    - host: 172.16.0.103
      user: "username3:password3"
...

The corresponding environment variable may look similar as a single comma-delimited string with syntax "host:username:password":

export MAGELLAN_COLLECT_LOGIN="172.16.0.101:username1:password1,172.16.0.102:username2:password2,172.16.0.103:username3:password3"

And finally, the CLI flags:

./magellan collect \
    --login "172.16.0.101:username1:password1" \
    --login "172.16.0.102:username2:password2" \
    --login "172.16.0.103:username3:password3"

The new method would obsolete the old --username and --password flags in favor of a single --login flag instead.

Other Considerations

Specifying the login information in the config file may not be ideal unless the config file exists in a location that requires elevated admin privileges. Therefore, it may be more advantageous to use environment variables or CLI flags as mentioned above in the "Possible Solutions" section.

Migrated from https://github.com/bikeshack/magellan/issues/6.