Moved init_conf call and preserve tempest network objects

Fixes race condition where configuation is accessed
before it is configured.

Preserve ports and subnets for tempest.conf networks.

Devstack creates private and public networks, and ports
and subnets in these networks. Cleanup needs to preserve
these objects unless --delete-tempest-conf-objects flag
is used.

Also removed unnecessary argument and updated doc string.

Change-Id: I30381191fde36aa71639a4aac3a4ca18a0733052
Cleanup class resources for large-ops scenario

Large Ops scenario is design to test the bulk creation of VMs while multiple
VMs already exist in tenant.
Due to some refactoring in Tempest scenario, the VMs are now deleted at the end
of the individual test cases.

Removes usage of addCleanup() from large-ops scenario.

Adds Class level method - addCleanupClass to cleanup resources at the end of
the test class.

Closes-Bug: #1395759
Change-Id: I612fcfab83a2046b8e597e009e385d7918f943b9
Remove not used attribute _schema_file

This was actually a remaining of [1].

[1]: https://review.openstack.org/#/c/115918

Change-Id: Idcf589fa9d89c2969914ef0c8aee27a22325470e
Adapt negative testing documentation

 - Removes the json file documentation
 - Removes XML part

Change-Id: I6a7fdcb12c84189f9adde6f83fee8b303c28a4ee
Merge "Moved init_conf call and preserve tempest network objects"
Merge "Remove not used attribute _schema_file"
Merge "Adapt negative testing documentation"
Merge "Cleanup class resources for large-ops scenario"
Merge branch 'master' of https://github.com/openstack/tempest