Update server_kwargs to boot_server_kwargs

Update server_kwargs to boot_server_kwargs

It takes into account "Remove deprecated stuff. Part 1" [1] and then fixes
rally_sanity and rally_full
(NovaKeypair.boot_and_delete_server_with_keypair [2])

[1] https://github.com/openstack/rally-openstack/commit/4436258d8fbb758a1771f908726e78c29e309c8a#diff-a80e66732701c545c7fc540d02ee1066
[2] http://artifacts.opnfv.org/functest/HG7XUW226S1T/functest-opnfv-functest-smoke-latest-rally_sanity-run-687/rally_sanity/rally_sanity.html#/NovaKeypair.boot_and_delete_server_with_keypair/failures

Change-Id: Id39b3231153efcccd58ed6bd988e26e2a672825b
Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>