DNSMasqServer.dnsmasq_fails_and_throws - intermittent failure

[Saviq]

From this master run:

[ RUN      ] DNSMasqServer.dnsmasq_fails_and_throws
/root/parts/multipass/src/tests/test_dnsmasq_server.cpp:151: Failure
Expected: dns.check_dnsmasq_running() throws an exception of type std::runtime_error.
  Actual: it throws nothing.
[  FAILED  ] DNSMasqServer.dnsmasq_fails_and_throws (10 ms)
[----------] 8 tests from DNSMasqServer (84 ms total)

[Saviq]

<greyback> hmm DNSMasqServer.dnsmasq_fails_and_throws appears to be unstable test, failing randomly on me

[gerboland]

Digging I see that in DNSMasqServer::check_dnsmasq_running that the race is with the get_dnsmasq_pid/kill branch, so must be a race in the PID file cleanup.