ipmi_client.robot to use new create_ipmi_ext_command_string
ipmi_client.robot to use new create_ipmi_ext_command_string

- Changed the 'external' IPMI functions to use new
  create_ipmi_ext_command_string and to forego the use of the old
  IPMI_EXT_CMD global variable.
- Changed 'Run External IPMI Raw Command' to simply call
  'Run External IPMI Standard Command'.
Also:
- Coding standards:
  - 2 blank lines betweeen keywords
  - Consistency: Changed many keyword argument names "args" to "command".
  - Added "Description of argument(s):"
  - Indented if/else body code

Change-Id: If2c1d6c3e2fbf438e17dc1e125937f76a5bde2b3
Signed-off-by: Michael Walsh <10404802c7de463f402c4a18638106ca1b12ef61@us.ibm.com>

openbmc/openbmc-test-automation,openbmc/openbmc-test-automation