[2.2] No enlistment error message when i386 are only available, but machine tries to PXE amd64 images

1. Imported i386 image
2. PXE booted machine via Legacy
3. No error messages shown even though we know we try to pxe boot amd64.

MAAS doesn't show any error messages that the amd64 image is not present. Only the i386 image is present. Judging by the looks.

==> /var/log/maas/rackd.log <==
2017-03-23 11:03:42 provisioningserver.rackdservices.tftp: [info] pxelinux.0 requested by b8:ae:ed:7d:06:2d
2017-03-23 11:03:42 provisioningserver.rackdservices.tftp: [info] pxelinux.0 requested by b8:ae:ed:7d:06:2d
2017-03-23 11:03:42 provisioningserver.rackdservices.tftp: [info] ldlinux.c32 requested by b8:ae:ed:7d:06:2d
2017-03-23 11:03:42 provisioningserver.rackdservices.tftp: [info] pxelinux.cfg/003cb529-7291-e411-87bf-b8aeed7d062d requested by b8:ae:ed:7d:06:2d
2017-03-23 11:03:42 provisioningserver.rackdservices.tftp: [info] pxelinux.cfg/01-b8-ae-ed-7d-06-2d requested by b8:ae:ed:7d:06:2d
2017-03-23 11:03:42 provisioningserver.rackdservices.tftp: [info] pxelinux.cfg/0A5A5ABE requested by b8:ae:ed:7d:06:2d
2017-03-23 11:03:42 provisioningserver.rackdservices.tftp: [info] pxelinux.cfg/0A5A5AB requested by b8:ae:ed:7d:06:2d
2017-03-23 11:03:42 provisioningserver.rackdservices.tftp: [info] pxelinux.cfg/0A5A5A requested by b8:ae:ed:7d:06:2d
2017-03-23 11:03:42 provisioningserver.rackdservices.tftp: [info] pxelinux.cfg/0A5A5 requested by b8:ae:ed:7d:06:2d
2017-03-23 11:03:42 provisioningserver.rackdservices.tftp: [info] pxelinux.cfg/0A5A requested by b8:ae:ed:7d:06:2d
2017-03-23 11:03:42 provisioningserver.rackdservices.tftp: [info] pxelinux.cfg/0A5 requested by b8:ae:ed:7d:06:2d
2017-03-23 11:03:42 provisioningserver.rackdservices.tftp: [info] pxelinux.cfg/0A requested by b8:ae:ed:7d:06:2d
2017-03-23 11:03:42 provisioningserver.rackdservices.tftp: [info] pxelinux.cfg/0 requested by b8:ae:ed:7d:06:2d
2017-03-23 11:03:42 provisioningserver.rackdservices.tftp: [info] pxelinux.cfg/default requested by b8:ae:ed:7d:06:2d
2017-03-23 11:03:43 provisioningserver.rackdservices.tftp: [info] ifcpu64.c32 requested by b8:ae:ed:7d:06:2d
2017-03-23 11:03:43 provisioningserver.rackdservices.tftp: [info] libcom32.c32 requested by b8:ae:ed:7d:06:2d
2017-03-23 11:03:43 provisioningserver.rackdservices.tftp: [info] ubuntu/amd64/generic/xenial/daily/boot-kernel requested by b8:ae:ed:7d:06:2d

==> /var/log/maas/regiond.log <==
2017-03-23 11:03:43 maasserver.region_controller: [info] Successfully configured DNS.
2017-03-23 11:04:01 twisted.python.log: [info] ::ffff:10.90.90.1 - - [23/Mar/2017:15:04:01 +0000] "GET /MAAS/rpc/ HTTP/1.0" 200 588 "-" "provisioningserver.rpc.cl
usterservice.ClusterClientService"
2017-03-23 11:04:13 maasserver.region_controller: [info] Successfully configured DNS.
2017-03-23 11:04:14 maasserver.dhcp: [info] Successfully configured DHCPv4 on rack controller 'tacp8y'.
2017-03-23 11:04:14 maasserver.dhcp: [info] Successfully configured DHCPv6 on rack controller 'tacp8y'.
2017-03-23 11:04:31 twisted.python.log: [info] ::ffff:10.90.90.1 - - [23/Mar/2017:15:04:30 +0000] "GET /MAAS/rpc/ HTTP/1.0" 200 588 "-" "provisioningserver.rpc.cl
usterservice.ClusterClientService"
2017-03-23 11:05:01 twisted.python.log: [info] ::ffff:10.90.90.1 - - [23/Mar/2017:15:05:00 +0000] "GET /MAAS/rpc/ HTTP/1.0" 200 588 "-" "provisioningserver.rpc.cl
usterservice.ClusterClientService"
2017-03-23 11:05:31 twisted.python.log: [info] ::ffff:10.90.90.1 - - [23/Mar/2017:15:05:30 +0000] "GET /MAAS/rpc/ HTTP/1.0" 200 588 "-" "provisioningserver.rpc.cl
usterservice.ClusterClientService"