Avoid N+1 in get_selected_hosts
Avoid N+1 in get_selected_hosts

`.load_ar_obj` will defer to `.load_ar_objs` when it is passed an array,
which will do a `.collect` call to `load_ar_obj` in return.  This is a
typical N+1, so this change takes the constantize code from
`.load_ar_obj` and applies it to the `allowed_hosts` to make a single
SQL call to for the needed hosts.

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