Remove context passing around, use climate.context instead

Since we have a global context storage we should use it everywhere. I
suggest we remove all this ctx args and never bring them back.
In case someone wants to run something with different context one can
always do:

    with my_other_context:
        run_method_without_ctx_in_args()

Change-Id: I976726f59cedd79f1d619f35f570c60e2c701c7d