[configdb] fix bug of leaving unwanted columns in a hash

[ishidawataru]

Current implementation doesn't remove unwanted columes with set_entry
like below.

>>> set_entry('table', 'key', {'key1': 'value1', 'key2': 'value2'})
>>> set_entry('table', 'key', {'key1': 'value3'})
>>> get_entry('table', 'key')
{'key1': 'value3', 'key2': 'value2'}

This commit fix this bug.

Signed-off-by: Wataru Ishida ishida.wataru@lab.ntt.co.jp

[ishidawataru]

I found #15 solves the same issue in a different way.

#15 is more lightweight but needs to explicitly specify the keys for removal.
The fix I made doesn't need to specify the keys for removal but needs to retrieve the original data.

[stcheng]

@taoyl-ms please check.
I don't think this is a bug. When we try to set an attribute with a new value, the current design is that we don't need to provide the rest of the attributes to replace the whole key-value tuple. The #15 will be enough for removing unwanted key-value tuples. However, I think there is a need to add the remove/del function to del an attribute-value tuple.
The logic here shall be similar to the concepts in SAI.

[lguohan]

set api usually does @ishidawataru says, we need to add a mod_entry API to explicit modify the field.