backend-tests/run: fix whitespace/quoted parameter handling
backend-tests/run: fix whitespace/quoted parameter handling

allow clients to pass arguments like -k 'not multitenant' or
-k "not multitenant" without any special tricks.

this requires mostly wrapping whitespace args in additional quotes,
and some extra parameter expansion magic.

changelog: none

Signed-off-by: mchalczynski <3a897b56ed6fc284ae11e3e7ec3ea48d098a7178@rndity.com>

pasinskim/integration,pasinskim/integration,pasinskim/integration