Refactoring codes and support complex virt-sandbox options testing

The current test framework doesn't support complex options testing of virt-sandbox, for example,
```python
1. virt-sandbox -c lxc:/// -n foo -N "dhcp,source=default" -N "dhcp,mac=00:44:33:22:11:55" -N "address=192.168.122.100/24,route=0.0.0.0/24%192.168.122.1" -- /usr/sbin/ip link show

2. virt-sandbox -c lxc:/// -n foo -m "host-bind:/tmp=/var/lib"  -i "/tmp" -m "ram:/tmp=500M" -- /usr/bin/mount
```

The patch is used for solving above issues, and can get an expected result, BTW, the patch 2 can be dropped, it just verifies whether the patch 1 works well, and then we should have a unit test for testing sandbox framework later.

$ ./run -t lvsb --test type_specific.lvsb_complex_options.positive_testing --no-download --keep-image
```python
SETUP: PASS (0.10 s)
DATA DIR: /var/lib/virt_test
DEBUG LOG: /home/ajia/Workspace/virt-test/logs/run-2014-01-08-18.05.02/debug.log
TESTS: 2
(1/2) type_specific.lvsb_complex_options.positive_testing.complex1: PASS (0.80 s)
(2/2) type_specific.lvsb_complex_options.positive_testing.complex2: PASS (0.71 s)
TOTAL TIME: 1.61 s
TESTS PASSED: 2
TESTS FAILED: 0
SUCCESS RATE: 100.00 %
```

$ grep "Launching" /home/ajia/Workspace/virt-test/logs/run-2014-01-08-18.05.02/debug.log
```python
18:05:02 DEBUG| Launching /usr/bin/virt-sandbox -c lxc:/// -n SCB_1 -N dhcp,source=default -N dhcp,mac=00:44:33:22:11:55 -N address=192.168.122.100/24,route=0.0.0.0/24%192.168.122.1 -- /usr/sbin/ip link show
18:05:03 DEBUG| Launching /usr/bin/virt-sandbox -c lxc:/// -n SCB_2 -m host-bind:/tmp=/var/lib -i /tmp -m ram:/tmp=500M -- /usr/bin/mount
```

$ cat lvsb/tests/cfg/lvsb_complex_options.cfg
```python
- lvsb_complex_options:
    type = lvsb_complex_options
    virt_test_type = lvsb
    variants:
        - positive_testing:
            status_error = "no"
            # Allows iterating times for the same option
            lvsb_opts_count = 2
            # The options look like lvsb_$name_options$num, the $num is an integer,
            # for $name, please refer to options naming convention in virttest/lvsb_base.py
            variants:
                - complex1:
                    # Allows iterating times for the same option
                    lvsb_opts_count = 3
                    # e.g. -N "dhcp,source=default" -N "dhcp,mac=00:44:33:22:11:55" -N "address=192.168.122.100/24,route=0.0.0.0/24%192.168.122.1"
                    lvsb_network_options1 = "dhcp,source=default"
                    lvsb_network_options2 = "dhcp,mac=00:44:33:22:11:55"
                    lvsb_network_options3 = "address=192.168.122.100/24,route=0.0.0.0/24%192.168.122.1"
                    lvsb_command = "/usr/sbin/ip link show"
                - complex2:
                    # The final options look like -m "host-bind:/tmp=/var/lib" -m "ram:/tmp=500M" -i "/tmp"
                    lvsb_mount_options1 = "host-bind:/tmp=/var/lib"
                    lvsb_mount_options2 = "ram:/tmp=500M"
                    lvsb_include_options1 = "/tmp"
                    lvsb_command ="/usr/bin/mount"
```