Awful performance rendering templates with ec2tag function in non-aws environments

[hairyhenderson]

For the Ec2Meta group of template functions, there's a 500ms timeout on the HTTP client: https://github.com/hairyhenderson/gomplate/blob/master/aws/ec2meta.go#L56, but for the Ec2Info functions (i.e. the ones that use aws-sdk-go), no such timeout is set, and I've been observing up to 20s timeouts.

For example:

$ docker run -it --rm --entrypoint '' hairyhenderson/gomplate bash
root@dde9d13c242b:/go/src/app# echo '{{ec2region}}' > r.json
root@dde9d13c242b:/go/src/app# echo '{{ec2tag "foo"}}' > t.json
root@dde9d13c242b:/go/src/app# time gomplate < r.json 
unknown

real	0m0.511s
user	0m0.000s
sys	0m0.010s
root@dde9d13c242b:/go/src/app# time gomplate < t.json 


real	0m20.901s
user	0m0.010s
sys	0m0.000s

Note that this doesn't always happen -- when I run on my mac, ec2tag times out quickly:

$ echo '{{ec2region}}' | time gomplate
unknown
gomplate  0.01s user 0.00s system 2% cpu 0.518 total
$ echo '{{ec2tag "foo"}}' | time gomplate

gomplate  0.01s user 0.01s system 1% cpu 0.897 total

Note that this is still longer than 500ms...