Dynamically populate pmdapapi metric table based on available metrics

We should fill in the 'metrictab' variable dynamically, based on the
metrics we observe during initialization.  This allows us to avoid
having a giant table of all possible papi metrics.
Remove unused gid references

We only run checks for uid's so remove the gid fields and update
the variable names accordingly
Add papi.control.enable_multiplexing metric to allow value based enablement

qa/914.out - update current testcase
src/pmdas/papi/help - add help text
src/pmdas/papi/papi.c - add functionality and new metric
src/pmdas/papi/pmdapapi.1 - update documentation
src/pmdas/papi/pmns - update papi.control namespace and add metric
Update multiplexing metric to papi.control.multiplex

Shorten the metric name, update docs, pmns, qa accordingly
papi pmda: tweak metric units

Some of the papi.* metric units can be more precise:

papi.system.* counters      to signed 64-bit and Units: count
papi.available.num_counters to Units: count
papi.control.auto_enable    left as is
papi.control.enable etc.    to Units: none

Conflicts:
	src/pmdas/papi/papi.c
Merge branch 'lberk/papi' of git://sourceware.org/git/pcpfans into dev

Conflicts:
	src/pmdas/papi/papi.c
qa: update 361 to handle revisions to cgroups metrics

Found a machine without active cgroups, needed for this test.
Reworked many parts to reflect cgroups-within-instances rather
than cgroups in metric names.
qa: resolve uninitd memory use in cgroups memory metrics

Noticing some indeterminism in results coming back for memory
metrics in 730,731 - turned out to be two issues.  Firstly we
were passing back uninitd memory under certain conditions, if
the stats file wasn't found and secondly we used an incorrect
path component.  Updated, and these tests are now stable.