tests: fix checking of ping return code
tests: fix checking of ping return code

Switch ==1 to !=0 - ping can exit with different errors (timeout,
resolve failed etc), but we don't care what was the reason.

QubesOS/qubes-core-admin,QubesOS/qubes-core-admin,marmarek/qubes-core-admin,woju/qubes-core-admin,QubesOS/qubes-core-admin,marmarek/qubes-core-admin,woju/qubes-core-admin,woju/qubes-core-admin,marmarek/qubes-core-admin,woju/qubes-core-admin