Fix: Use temporary_key_pair_name when specified.
This is to fix an issue where the temporary_key_pair_name configuration option
for amazon-ebs and amazon-instance builders would be ignored and replaced with
an automatically generated value using UUID, even when the option was explicitly
specified.
Remove space from the auto-generated SSH key-pair name.
Resolves#3736
/cc @whostolebenfrog - I actually simplified things quite a bit. I added
a "uuid" global template function so it just uses that now. I renamed it
so that it is clear it is a temporary keypair.