pldm_visualise_pdrs.py: add support for ssh_config
pldm_visualise_pdrs.py: add support for ssh_config

Add support for parsing user ssh_configs.  For now, this lets users
specify an ssh_config host entry with the --bmc parameter and the script
will pick up the hostname and user directives if they are specified in
the host entry.  Like ssh itself, a --user option on the command line
overrides any user specified in the ssh_config host entry.

Change-Id: I4d564677424e984de033a1d15ca6d51342091772
Signed-off-by: Brad Bishop <713d098c0be4c8fd2bf36a94cd08699466677ecd@fuzziesquirrel.com>

openbmc/pldm,openbmc/pldm,openbmc/pldm