cli: "result show": Add --no-merge-rolemap option

The new resultstore schema enables different benchmark roles to execute
on different nodes of a SUT in parallel. The mapping of roles to nodes
is done with a rolemap.

This addition means it is possible for the same benchmark to run on the
same SUT with with a different mapping of it's roles to nodes. By
default, we just aggregate all results for a given benchmark targeting a
given SUT to generate the summary statistics. But due to different
rolemaps, this may not always be desirable. Clearly if you're comparing
a benchmark across different SUTs, then by definition the rolemap will
be different for each case and it makes sense to merge (the default).
But if comparing a benchmark across different swprofiles all on the same
SUT it may be preferable to avoid merging different rolemaps.

Add --no-merge-rolemap option to disable this merging behavior. When
present, an additional column "Role Map" is added to the output table to
identify the rolemap for which the results were aggregated.

Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>