test: allow taking extra arguments from environment

test: allow taking extra arguments from environment

When running unit tests automatically, either via script, from meson,
or otherwise, the same set of options may be used for each run, for
example to set a standard coremask to be used for all tests.

To facilitate this, this patch adds support for the test binary taking
additional EAL parameters from the environment and appending them to the
argc/argv list passed to eal init. This allows parameter modification
without having to edit test scripts etc.

There are now two environment variables which can be used for running
tests:
 * DPDK_TEST - (added previously) passes the test name to be run
               automatically rather than running the app interactively.
               Used by "meson test" when running tests individually or
               as part of a suite.

 * DPDK_TEST_PARAMS - new parameter to specify the commandline arguments
               to use with the test binary. For example to run a test,
               or tests, on only 16 lcores, and to skip pci scan we can
               set this to "-l 0-15 --no-pci".

Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
Tested-by: Luca Boccassi <bluca@debian.org>