pmwebd: improve /metrics/find emulation for graphite dashboard

Comparing a live graphite installation to pmwebd's emulation, it
showed that a small tweak to the JSON result formatting was sufficient
to get the basic graphite-side dashboard working.  Further tweaking
made it possible to expand wildcards throughout the graphite metric
string in a compatible manner.  (The grafana interactive metric
builder is affected, and keeps working.)  A further tweak lets pmwebd
tolerate the graphite dashboard webapp's tendency to use
non-/graphite-prefixed URLs to do its work.
papi pmda: auto-enable error path

Let's not neglect to propagate refresh_metrics() errors
for auto-enabled counters to fetching pcp clients.
papi 5.4.0 rebuild.
Merge branch 'fche/dev' into merge
build: add .gitignore file for perfevent pmda
qa: begin a collection of /proc/cpuinfo files for testing

A set of /proc/cpuinfo files from various architectures and
with varying CPU counts, for exercising hinv.cpu.* metrics.
Thanks to everyone who's sent some through so far, keep 'em
rolling in please!
pmda proc: fix cgroup fd leaks causing too many open files