fix(tests): plethora of fixes to functional tests

- remove update-ca-certificates from node start, dramatically reducing
  container spin-up time
- removing time.Sleep when spinning up a node; instead, poll until
  it looks like the container is fully booted
- cleaning up network interfaces more thoroughly between tests,
  preventing a race where one test failure will cause a cascading
  failure in subsequent tests
- copies /etc/nsswitch.conf into container to ensure users are available
  during startup (in the non-container world this is handled by initrd)
Merge pull request #537 from jonboulle/functional_functional

fix(tests): plethora of fixes to functional tests