debuginfod test: fix groom/stale race condition

debuginfod test: fix groom/stale race condition

Additional tracing, and use of "% make check VERBOSE=1" in a .spec
file allowed tracking down of this intermittent problem.  The race was
between a SIGUSR1 or two to a debuginfod server (triggering two
traverse/scan phases), followed shortly by a SIGUSR2 (triggering a
groom).  If those signals were received too close together, the groom
phase could be stopped early, and the rm'd files not noticed.

New testsuite code adds metric polls after SIGUSR1 & SIGUSR2 to ensure
the respective processing phases are complete.  It also turns on "set -x"
tracing, so as to avoid pulling out quite as much hair next time.
"make check VERBOSE=1" is also important for spec files.

Signed-off-by: Frank Ch. Eigler <fche@redhat.com>