Make destroying guest_devices faster
Make destroying guest_devices faster

GuestDevice.destroy() was extremely slow, and was doing an extra:
```
[----] D, [2019-08-30T15:59:25.111041 #6727:2ad6e77ec5b4] DEBUG -- :    (380.0ms)  SELECT "guest_devices"."id" FROM "guest_devices"
```

which was taking forever.

Switching to .delete and manually dependent destroying the guest_device
dependent records was much faster.

juliancheal/manageiq,pkomanek/manageiq,gmcculloug/manageiq,mkanoor/manageiq,chessbyte/manageiq,d-m-u/manageiq,agrare/manageiq,borod108/manageiq,jrafanie/manageiq,billfitzgerald0120/manageiq,lpichler/manageiq,hstastna/manageiq,djberg96/manageiq,mzazrivec/manageiq,tinaafitz/manageiq,jrafanie/manageiq,juliancheal/manageiq,aufi/manageiq,jvlcek/manageiq,tinaafitz/manageiq,chessbyte/manageiq,aufi/manageiq,kbrock/manageiq,agrare/manageiq,hstastna/manageiq,billfitzgerald0120/manageiq,skateman/manageiq,ManageIQ/manageiq,ManageIQ/manageiq,hstastna/manageiq,ManageIQ/manageiq,hstastna/manageiq,borod108/manageiq,borod108/manageiq,jvlcek/manageiq,aufi/manageiq,djberg96/manageiq,NickLaMuro/manageiq,jvlcek/manageiq,ManageIQ/manageiq,djberg96/manageiq,NickLaMuro/manageiq,NickLaMuro/manageiq,kbrock/manageiq,gmcculloug/manageiq,tinaafitz/manageiq,billfitzgerald0120/manageiq,chessbyte/manageiq,skateman/manageiq,mzazrivec/manageiq,pkomanek/manageiq,agrare/manageiq,lpichler/manageiq,juliancheal/manageiq,NickLaMuro/manageiq,lpichler/manageiq,mkanoor/manageiq,skateman/manageiq,mzazrivec/manageiq,gmcculloug/manageiq,d-m-u/manageiq,d-m-u/manageiq,billfitzgerald0120/manageiq,jvlcek/manageiq,djberg96/manageiq,mzazrivec/manageiq,chessbyte/manageiq,aufi/manageiq,kbrock/manageiq,agrare/manageiq,kbrock/manageiq,lpichler/manageiq,pkomanek/manageiq,d-m-u/manageiq,mkanoor/manageiq,borod108/manageiq,jrafanie/manageiq,skateman/manageiq,mkanoor/manageiq,tinaafitz/manageiq,gmcculloug/manageiq,jrafanie/manageiq,pkomanek/manageiq,juliancheal/manageiq