twister: BinaryHandler: call try_kill_process_by_pid in a 'with' scope

The commit
531fe89e (sanitycheck: use multiprcoessing instead of threads)
introduce regression for ARC nsim_hs_smp platform.

The regression is that verification on nsim_hs_smp hangs. That
happens because now we don't call try_kill_process_by_pid()
in the 'with' scope of the 'subprocess.Popen' when we spawning
BinaryHandler thread. Previously it was called via `terminate`
method of `BinaryHandler` but it was changed in 531fe89e.
So if we can't terminate the simulator in a normal way
(which is expected for 'mdb' which is used for nsim_hs_smp
simulation) we will hang forever - we will never return from
'with' scope of the 'subprocess.Popen' as we are waiting for
process termination but the try_kill_process_by_pid() is located
latter and we never reach it.

Fix that.

Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>