add: exclude file support

This patch allow to run tempest-report with --full-run option and to
provide an exclude file where some tests won't be run.

So it add an --exclude option where we have to specify an exclude file.

Example of use:
tempest-report --full-run --exclude my_exclude_tests

Syntax of exclude file:
----
test_create_server
test_virtual_interfaces.VirtualInterfacesTestJSON
test_nova_manage.SimpleReadOnlyNovaManageTest.test_cell_list
---

It will delete all tests containing the content of each line and run all
others.

implement feature #2
Signed-off-by: Emilien Macchi <emilien.macchi@enovance.com>