tests: cpus awareness

tests: cpus awareness

Introduce MAX_CPUS parameters to control maximum number of CPUs used by
VPP(s) during testing, with default value 'auto' corresponding to all
CPUs available.

Calculate test CPU requirements by taking into account the number of
workers, so a test requires 1 (main thread) + # of worker CPUs.

When running tests, keep track of both running test jobs (controlled by
TEST_JOBS parameter) and free CPUs. This then causes two limits in the
system - to not exceed number of jobs in parallel but also to not exceed
number of CPUs available.

Skip tests which require more CPUs than are available in system (or more
than MAX_CPUS) and print a warning message.

Type: improvement
Change-Id: Ib8fda54e4c6a36179d64160bb87fbd3a0011762d
Signed-off-by: Klement Sekera <ksekera@cisco.com>