added defaultDeploymentRepo on RepositoryVirtual

[PatriceG]

I added support to set the default deployment repo name, that we need.
It's fixing issue #460

[beliaev-maksim]

also need tests for this

[PatriceG]

sorry indeed it should be
self.default_deployment_repo_name = default_deployment_repo_name

I pushed a fix.

I'm not sure I understand how to setup a test environment for your lib.

[beliaev-maksim]

please provide a unittest with mocks, we use responses

[PatriceG]

I'm not familiar with mocking in Python.
I'm not sure I understand how to setup a test environment for your lib.
I just wanted to contribute this fix in the lib (I do have a workaround by sublcassing the RepositoryVirutal class but it's not ideal).

[beliaev-maksim]

these are the classic unit tests:
https://github.com/devopshq/artifactory/blob/master/docs/CONTRIBUTE.md#unit

then you can see the unit folder and add new tests similar to other

[PatriceG]

There is not a single existing unit test for RepositoryLocal and Virtual.
I'm sorry I have no time to try to understand how to setup a test env.
Feel free to reject my PR if you like. I can do with my local modifications. I just wanted to simply contribute.