test: hsr: Extract version agnostic information from ping command output

Current code checks if ping command output match hardcoded pattern:
"10 packets transmitted, 10 received, 0% packet loss,".

Such approach will work only from one ping program version (for which
this test has been originally written).
This patch address problem when ping with different summary output
like "10 packets transmitted, 10 packets received, 0% packet" is
used to run this test - for example one from busybox (as the test
system runs in QEMU with rootfs created with buildroot).

The fix is to modify output of ping command to be agnostic to ping
version used on the platform.

Signed-off-by: Lukasz Majewski <lukma@denx.de>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>