OK, I reproduced the error again. Here's some further info:

https://gist.github.com/mikemccracken/883f91e34c3eb8ee4b47#file-reproduced-with-further-info-md

In the middle of the machine-1.log, you see this:

2015-11-04 22:48:33 DEBUG juju.container.lxc lxc.go:425 creating lxc container "juju-trusty-lxc-template"
2015-11-04 22:48:33 DEBUG juju.container.lxc lxc.go:426 lxc-create template params: [--debug --userdata /var/lib/juju/containers/juju-trusty-lxc-template/cloud-init --hostid juju-trusty-lxc-template -r trusty -T https://10.0.3.45:17070/environment/6337473f-b80a-4ed3-8a5b-9a789e3b25f9/images/lxc/trusty/amd64/ubuntu-14.04-server-cloudimg-amd64-root.tar.gz]
2015-11-04 22:48:33 TRACE golxc.run.lxc-create golxc.go:448 run: lxc-create [-n juju-trusty-lxc-template -t ubuntu-cloud -f /var/lib/juju/containers/juju-trusty-lxc-template/lxc.conf -- --debug --userdata /var/lib/juju/containers/juju-trusty-lxc-template/cloud-init --hostid juju-trusty-lxc-template -r trusty -T https://10.0.3.45:17070/environment/6337473f-b80a-4ed3-8a5b-9a789e3b25f9/images/lxc/trusty/amd64/ubuntu-14.04-server-cloudimg-amd64-root.tar.gz]
2015-11-04 22:48:33 TRACE golxc.run.lxc-create golxc.go:458 run failed output: + '[' amd64 = i686 ']'
+ '[' 0 = 0 ']'
+ case "$hostarch:$arch" in
+ :
+ '[' tryreleased '!=' daily -a tryreleased '!=' released -a tryreleased '!=' tryreleased ']'
+ '[' -z /var/lib/lxc/juju-trusty-lxc-template ']'
++ id -u
+ '[' 0 '!=' 0 ']'
+ config=/var/lib/lxc/juju-trusty-lxc-template/config
+ '[' -z /var/lib/lxc/juju-trusty-lxc-template/rootfs ']'
+ type ubuntu-cloudimg-query
ubuntu-cloudimg-query is /usr/bin/ubuntu-cloudimg-query
+ type wget
wget is /tmp/wget992629130/wget
+ cache=/var/cache/lxc/cloud-trusty
+ '[' 0 -eq 1 ']'
+ mkdir -p /var/cache/lxc/cloud-trusty
+ '[' tryreleased = tryreleased ']'
+ stream=released
+ ubuntu-cloudimg-query trusty released amd64
+ '[' -n https://10.0.3.45:17070/environment/6337473f-b80a-4ed3-8a5b-9a789e3b25f9/images/lxc/trusty/amd64/ubuntu-14.04-server-cloudimg-amd64-root.tar.gz ']'
+ url2=https://10.0.3.45:17070/environment/6337473f-b80a-4ed3-8a5b-9a789e3b25f9/images/lxc/trusty/amd64/ubuntu-14.04-server-cloudimg-amd64-root.tar.gz
++ basename https://10.0.3.45:17070/environment/6337473f-b80a-4ed3-8a5b-9a789e3b25f9/images/lxc/trusty/amd64/ubuntu-14.04-server-cloudimg-amd64-root.tar.gz
+ filename=ubuntu-14.04-server-cloudimg-amd64-root.tar.gz
+ '[' -n https://10.0.3.45:17070/environment/6337473f-b80a-4ed3-8a5b-9a789e3b25f9/images/lxc/trusty/amd64/ubuntu-14.04-server-cloudimg-amd64-root.tar.gz ']'
+ do_extract_rootfs
+ cd /var/cache/lxc/cloud-trusty
+ '[' 0 -eq 1 ']'
+ trap wgetcleanup EXIT SIGHUP SIGINT SIGTERM
+ '[' '!' -f ubuntu-14.04-server-cloudimg-amd64-root.tar.gz ']'
+ wget https://10.0.3.45:17070/environment/6337473f-b80a-4ed3-8a5b-9a789e3b25f9/images/lxc/trusty/amd64/ubuntu-14.04-server-cloudimg-amd64-root.tar.gz
--2015-11-04 22:48:33--  https://10.0.3.45:17070/environment/6337473f-b80a-4ed3-8a5b-9a789e3b25f9/images/lxc/trusty/amd64/ubuntu-14.04-server-cloudimg-amd64-root.tar.gz
Connecting to 10.0.3.45:17070... connected.
ERROR: no certificate subject alternative name matches
	requested host name '10.0.3.45'.
To connect to 10.0.3.45 insecurely, use `--no-check-certificate'.


#### note from Mike: the rest is just a cascading error:

+ build_root_tgz ubuntu-14.04-server-cloudimg-amd64-root.tar.gz
+ url=ubuntu-14.04-server-cloudimg-amd64-root.tar.gz
+ filename=
++ mktemp -d -p .
+ xdir=./tmp.OdTAAQuXxT
++ basename ubuntu-14.04-server-cloudimg-amd64-root.tar.gz
+ tarname=ubuntu-14.04-server-cloudimg-amd64-root.tar.gz
+ imgname='trusty-*-cloudimg-amd64.img'
+ trap buildcleanup EXIT SIGHUP SIGINT SIGTERM
+ '[' 0 -eq 1 -o '!' -f /var/cache/lxc/cloud-trusty/ubuntu-14.04-server-cloudimg-amd64-root.tar.gz ']'
+ rm -f ubuntu-14.04-server-cloudimg-amd64-root.tar.gz
+ echo 'Downloading cloud image from ubuntu-14.04-server-cloudimg-amd64-root.tar.gz'
Downloading cloud image from ubuntu-14.04-server-cloudimg-amd64-root.tar.gz
+ wget ubuntu-14.04-server-cloudimg-amd64-root.tar.gz
--2015-11-04 22:48:33--  http://ubuntu-14.04-server-cloudimg-amd64-root.tar.gz/
Resolving ubuntu-14.04-server-cloudimg-amd64-root.tar.gz (ubuntu-14.04-server-cloudimg-amd64-root.tar.gz)... failed: Name or service not known.
wget: unable to resolve host address 'ubuntu-14.04-server-cloudimg-amd64-root.tar.gz'
+ echo 'Couldn'\''t find cloud image ubuntu-14.04-server-cloudimg-amd64-root.tar.gz.'
Couldn't find cloud image ubuntu-14.04-server-cloudimg-amd64-root.tar.gz.
+ exit 1
+ buildcleanup
+ cd /var/lib/lxc/juju-trusty-lxc-template/rootfs
+ umount -l /var/cache/lxc/cloud-trusty/./tmp.OdTAAQuXxT
umount: /var/cache/lxc/cloud-trusty/./tmp.OdTAAQuXxT: not mounted
+ true
+ rm -rf /var/cache/lxc/cloud-trusty
lxc_container: lxccontainer.c: create_run_template: 1125 container creation template for juju-trusty-lxc-template failed
lxc_container: lxc_create.c: main: 271 Error creating container juju-trusty-lxc-template