Support openssh option format

[mrkschan]

According to man ssh_config of openssh, the option format follows.

     Empty lines and lines starting with ‘#’ are comments.  Otherwise a line is of the format
     “keyword arguments”.  Configuration options may be separated by whitespace or optional
     whitespace and exactly one ‘=’; the latter format is useful to avoid the need to quote
     whitespace when specifying configuration options using the ssh, scp, and sftp -o option.
     Arguments may optionally be enclosed in double quotes (") in order to represent arguments
     containing spaces.