* When the value contains space in machine.conf and does not have
  double quote, "install.sh" can't correctly read it.

* "install.sh" uses dot command(i.e. source) to apply the settings
  in machine.conf. If the value in machine.conf are separated by space
  without double quotes between them, it will return failure when
  install.sh try to source machine.conf.

```
machine.conf example:
  ...
  onie_disco_ntpsrv=10.254.141.10 10.254.141.131
  ...

install.sh returns:
  ...
  /tmp/tmp.A7wHuAMSQV/installer/install.sh: 11: /host/machine.conf: 10.254.141.131: not found
```

* Add a new function 'read_conf_file' to read the settings from
  machine.conf when the value in machine.conf are separated by space
  without double quotes between them.

* Originally, the script will failed if the line of machine.conf
  is comment line or blank line. After this patch, it can correctly
  handle these type of content.

Handle following types of line
* Whole comment line
* Comment string behind declaration
* Comment string behind some spaces
* Blank line

* To run this test, `cd` into the tests directory and `./test_read_conf.sh`

  If pass, it will return 0 and show "PASS".
  If fail, it will return 1 and show "[ERR] Expect value(x86_64) is not equal
  to input value()".