Test: Unmanaged: Replace ping command in tests with curl

[vipulgupta2048]

This change is required to migrate existing tests to run QEMU worker tests on GitHub Actions. GitHub hosted runners can't run the ping command: https://github.com/actions/runner-images/issues/1519 by design. If we still intend to use ping, the solution would be running QEMU worker tests on self-hosted runners which allow ICMP packets

This change is intended to be backwards compatible and shouldn't affect tests running on Jenkins or for the autokit

Change-type: patch Signed-off-by: Vipul Gupta (@vipulgupta2048) vipulgupta2048@gmail.com

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[vipulgupta2048]

@resin-jenkins retest this please