nuke: don't require noipmi in ctx
nuke: don't require noipmi in ctx

This is called from run.py too, which won't have ctx.noipmi.
The default of using impmi is fine for now for run.py.

Signed-off-by: Josh Durgin <51652c783f70f5b272ebd02f1fd20d3af7a2449f@inktank.com>

robbat2/teuthology,ceph/teuthology,t-miyamae/teuthology,zhouyuan/teuthology,yghannam/teuthology,michaelsevilla/teuthology,robbat2/teuthology,dmick/teuthology,t-miyamae/teuthology,caibo2014/teuthology,dreamhost/teuthology,SUSE/teuthology,tchaikov/teuthology,ktdreyer/teuthology,SUSE/teuthology,dreamhost/teuthology,yghannam/teuthology,zhouyuan/teuthology,ivotron/teuthology,michaelsevilla/teuthology,ktdreyer/teuthology,tchaikov/teuthology,ivotron/teuthology,dmick/teuthology,caibo2014/teuthology,ceph/teuthology,SUSE/teuthology,dmick/teuthology