Update LDMS Variorum sampler to support Variorum v0.8

[tpatki]

Work in Progress, not ready for review.

Fixes #1431.

This PR updates the JSON API and the parsing of power data based on Variorum 0.8.

ToDo:

• Code Formatting
• Documentation updates
• Squash commits
• Autoconf checks
• Testing (see below)

Testing:

• IBM Alehouse node, CPU+GPU build
• IBM Alehouse node, GPU-build only
• IBM Alehouse node, CPU-build only
• Other LLNL systems with @kshoga1 and @slabasan.

[morrone]

@tpatki Could you also please this squash this PR together into just a small set of clean commits?

You will also need to include appropriate autoconf checks since this will now only work with variorum 0.8 or newer.

[tpatki]

@morrone
Thanks for the quick feedback! :)

Yes, I will squash into clean commits when we're done testing and when I mark this as ready for review (will be a few weeks until @kshoga1 can test on Mutt.)

You will also need to include appropriate autoconf checks since this will now only work with variorum 0.8 or newer.

Could you please clarify this? We were not checking for a specific version in configure.ac here earlier. Where/how should we include the autoconf checks (is there an example we can follow)?

[morrone]

Could you please clarify this? We were not checking for a specific version in configure.ac here earlier. Where/how should we include the autoconf checks (is there an example we can follow)?

Better than a specific version check is to test for features in the library that the code requires. For instance, are there some unique new function in the new version of the library? You could add a test for that function in the library.

LDMS's configure.ac has an AC_LIB_HAVE_LINKFLAGS test for variorum. There is an additional "testcode" field for that macro where you could put a tiny bit of C code that calls a function that is unique to the newer version of the code.

https://www.gnu.org/software/gnulib/manual/html_node/Searching-for-Libraries.html