create_ami.sh.in is now static, uses a config file

instead of a template expecting to have arch, base, name,
and tarball variables substituted into it, this script
now optionally consumes a config file in current directory
(which is how it will be used by studio); all these values
can still be provided on the command line.
create_ami.sh.in -> create_ami.sh

it's not a template anymore, so the .in suffix makes no sense.
i didn't include this move in the previous commit to make the
code changes more visible.
--list-regions describes the available AWS regions

case statements in opensuse_set_aki_id and find_ami
look the same.
exit_if_failed explicit about $?, loses dead code
$EC2_CERT, $EC2_PRIVATE_KEY must be readable
ec2fe reduces duplication using ec2-whatever

all ec2-whatever invocation used --region $region, now this option
is packaged in the ec2fe function.  the first argument is the desired
command without the "ec2-" prefix, the rest is passed through.
do_ssh reduces duplication of ssh(1) options
opensuse_set_aki_id -> opensuse_find_aki

doesn't set anything, returns the value, client code need not
rely on global variables.
create_security_group a bit more straight-forward
reduced duplication in clean_up
create_ami.sh: simpler use of $isOpenSUSE

this variable is at all times either "true" or "false",
and these are actual commands.  no need to use test(1).