Replace test.attr with decorators.attr

Function 'tempest.test.attr()' has moved to 'tempest.lib.decorators
.attr()' in Pike and will be removed in a future version[1].
This patch replaces the 'tempest.test.attr()' with the 'tempest.lib
.decorators.attr().'

[1] Iaafbb112b6eee458089cc49918359a8a8d0485e2

Change-Id: I4796a1e10311cae2910e0d3ee5d0cb8368fbed1e
1 file changed