Host savenodes tests are unreliable

[halfalicious]

Hitting these failures intermittently for the Linux clang6 configuration in various PRs which don't touch code that is covered by the tests:

Test Case "saveNodes": 
/home/builder/project/test/unittests/libp2p/peer.cpp(188): error: in "libp2p/p2p/saveNodes": check host.peerCount() == c_peers has failed [0 != 5]
/home/builder/project/test/unittests/libp2p/peer.cpp(189): error: in "libp2p/p2p/saveNodes": check host2.peerCount() == c_peers has failed [4 != 5]
/home/builder/project/test/unittests/libp2p/peer.cpp(215): fatal error: in "libp2p/p2p/saveNodes": critical check r[2].itemCount() >= c_nodes has failed

*** 3 failures are detected (5 failures are expected) in the test module "Master Test Suite"