NSB support for [core x-y] NSB PROX NFVI configuration

JIRA: YARDSTICK-1571

Cores in PROX support multiple configurations

NSB supports today the more basic one, i.e. [core x]

When one wants to use multiple cores sharing the same
configuration, instead of copying the whole [core]
section, PROX support the following syntax

[core x-y]
where x is the 1st core and y the last one
or (for instance) [core x,y,z]

NSB Now supports

[core a,b,c,d]
[core a-d]
[core a,c-d]

Change-Id: I34cd107143c89e16d58e7a99e1887ffbf720a5d1
Signed-off-by: Daniel Martin Buckley <daniel.m.buckley@intel.com>