Kill whole process group when power commands terminate.

To make this work the MonitoredSubprocess was changes to be the
process group leader, rather than beaker-provision.

Bug: 1008509
Change-Id: I5fe0c1d2102cfea6a07ce159aef3c7d32c184e77
Use finer width resolution for recipe progress bar

Bug: 1014938
Change-Id: Ia81705ce2ce3eb28fb136f16e1fafa5954897555
fix access policy SQL migration

Now correctly adds 'reserve' permission for non-admin groups, and all
permissions for admin groups on non-shared systems.

The INSERT statements were also amended to avoid inserting duplicate
rules, so that they can safely be run multiple times or on databases
that have already been migrated before.

Bug: 1015328
Change-Id: I661953cee2eded42c86ea3bd75b1acc806024276
Merge branch 'release-0.15' into develop