Consider allowing numeric-form for enum command arguments

When sending commands via ait_cmd_send.py, for any enum based arguments, only the string name component is allowed. Consider allowing the numeric version to also be accepted.

Example of a command with integer and enum argument

- !Command
  name:      SEQ_ENABLE_DISABLE
  opcode:    0x0003
  subsystem: CMD
  title: Enable/Disable Sequence
  desc:      |
    This command enables or disabled the specified sequence.  If a
    sequence to be disabled is currently executing, it will be
    interrupted.

  arguments:
    - !Argument
      name:  sequence_id
      desc:  Sequence ID
      units: none
      type:  MSB_U16
      bytes: [0,1]

    - !Argument
      name:  enable
      desc:  Enable
      units: none
      type:  U8
      bytes: 2
      enum:
        0: DISABLED
        1: ENABLED

Using name version of enum:

>> $AIT_ROOT/ait/core/bin/ait_cmd_send.py SEQ_ENABLE_DISABLE 1 ENABLED
2019-06-26T17:16:16.575 | PROGRAM  | /Users/nttoole/dev/ait/git_repos/ait_052919/AIT-Core/ait/core/bin/ait_cmd_send.py SEQ_ENABLE_DISABLE 1 ENABLED
2019-06-26T17:16:16.577 | COMMAND  | Sending to 127.0.0.1:3075: SEQ_ENABLE_DISABLE 1 ENABLED
2019-06-26T17:16:16.579 | PROGRAM  | done.

Using numeric version of enum:

>> $AIT_ROOT/ait/core/bin/ait_cmd_send.py SEQ_ENABLE_DISABLE 1 1
2019-06-26T17:16:23.512 | PROGRAM  | /Users/nttoole/dev/ait/git_repos/ait_052919/AIT-Core/ait/core/bin/ait_cmd_send.py SEQ_ENABLE_DISABLE 1 1
2019-06-26T17:16:23.514 | ERROR    | enable value '1' not in allowed enumerated values.
2019-06-26T17:16:23.515 | PROGRAM  | done.

Start with ait/core/bin/ait_cmd_send.py and trace how enum-based command arguments are validated. Use the SEQ_ENABLE_DISABLE example to check that the numeric value 1 is accepted alongside ENABLED, while the existing command behavior remains intact.