Update subnet test to not use pre-created share network

This pathc updates 'test_delete_contains_shares' to not use
pre-created share network since the test may fail to delete the
share server and the share network subnet if more shares were
created using the same share network, by other concurrent tests.

Change-Id: I950560ac8040e8deadd21f869f04416153fd8a88
1 file changed