intel-xed and hpcviewer: adapt to new resource placement

[mwkrentel]

Change 'destination' to 'placement' in the use of resource() for
intel-xed and hpcviewer. Recent commits (1842873 and eb584d8)
changed the directory path for a resource and thus broke the build
for these packages.

[mwkrentel]

@tldahlgren @tgamblin
This is a followup to #11647 and #11666. I found a difference between
destination and placement in the use of resource().

In the intel-xed package, I use a resource that should be expanded as
the mbuild subdir in the main package (it used to be). With
destination, I get:

resource(name='mbuild',
         git='https://github.com/intelxed/mbuild.git',
         commit=mbuild_hash, destination='mbuild',
         when='@{0}'.format(vers))

==> Moving resource stage
        source : /home/krentel/binary/spack-repo/var/spack/stage/resource-mbuild-enp62qcq63ixph45z3a5z2yudehcdana/src/
        destination : /home/krentel/binary/spack-repo/var/spack/stage/intel-xed-2019.03.01-enp62qcq63ixph45z3a5z2yudehcdana/src/mbuild/src

Fails because the resource is in the wrong path.

Changing destination to placement, I get:

resource(..., placement='mbuild')

==> Moving resource stage
        source : /home/krentel/binary/spack-repo/var/spack/stage/resource-mbuild-enp62qcq63ixph45z3a5z2yudehcdana/src/
        destination : /home/krentel/binary/spack-repo/var/spack/stage/intel-xed-2019.03.01-enp62qcq63ixph45z3a5z2yudehcdana/src/mbuild

So, destination and placement put the mbuild directory in different
places.

Is this the intended semantics?

Anyway, assuming these semantics are intentional and stable going
forward, then I'd like to get this merged. This is currently a
blocker for building hpctoolkit.

And next time, I'd kinda like more of a heads up.

Btw, spack read-the-docs only mentions destination, not placement.

[tgamblin]

I'm merging this to unblock hpctoolkit, but @mwkrentel is right -- we should document and maybe fix the semantics for resource. destination and placement are kind of confusing and we either need clearer docs or a less confusing set of parameters. We should probably look at how these are used and see if we can simplify.