Although they normally work, some failures have been reported in the field
related to the MST hub not responding in the MST plugin.
When these failures have occurred the dell_dock plugin also fails to
enumerate.
So rather than allow some people who don't have dell_dock compiled to
update their MST hub using synaptics_mst, perform ALL updates for
mst hub via dell_dock.
```
18:06:24:0324 FuPluginSynapticsMST no device found on drm_dp_aux1: VMM5331 inside Dell dock is only supported by dell_dock
```
This flag is used internally by plugins to indicate that they will
skip the phase of firmware installation that power cycles a device.
It is intended to be set by quirks or other environment settings.
