* hcl2template: use && for chaining conditions
For deciding if we need to run an error provisioner block, we checked
using a nested if that we didn't need to avoid running it.
This is unnecessary, and adds a superfluous level of inbrication to the
code, so we chain both conditions with &&.
* hcl2: don't warn on excluded post-processor
When a post-processor is excluded through the -except command-line
argument for packer build, we used to print a warning on HCL2 templates
if this except statement did not match a build.
However, since we can use the except option to avoid running
post-processors, we should account for this as well when printing out a
warning that there were no matches.
This commit adds this counter to the except checks for the
post-processors as well.