Add the ability to update a user's password from the CLI

[russorat]

as a user
when i use the update capability of the cli
then i would like the ability to update the password of the user

we should add -p, --password option to set the password of the user.

➜  influxdb git:(master) ✗ ./bin/darwin/influx user update -i 050c7357c0e83000 -h
Update user

Usage:
  influx user update [flags]

Flags:
  -h, --help          Help for the update command
  -i, --id string     The user ID (required)
  -n, --name string   The user name

Global Flags:
      --host string    HTTP address of Influx (default "http://localhost:9999")
      --local          Run commands locally against the filesystem
      --skip-verify    SkipVerify controls whether a client verifies the server's certificate chain and host name.
  -t, --token string   API token to be used throughout client calls