Our test cases spew a lot of files and directories around $TMPDIR. Make more
thorough use of the testing package's TempDir methods to ensure these are
cleaned up.
In a few cases, this required plumbing test contexts through existing helper
code. In a couple places an explicit path was required, to work around cases
where we do global setup during a TestMain function. Those cases probably
deserve more thorough cleansing (preferably with fire), but for now I have just
worked around it to keep focused on the cleanup.
* Allow for zero witness providers
* Verify provider duplicates, fix tests
* Add duplicate provider ID to the error
* Return error on attempt to remove last witness
* Verify duplicates when restoring from store
*light: rpc /status returns status of light client ; code refactoring
light: moved lightClientInfo into light.go, renamed String to ID
test/e2e: Return light client trusted height instead of SyncInfo trusted height
test/e2e/start.go: Not waiting for light client to catch up in tests. Removed querying of syncInfo in start if the node is a light node
* light: Removed call to primary /status. Added trustedPeriod to light info
* light/provider: added ID function to return IP of primary and witnesses
* light/provider/http/http_test: renamed String() to ID()
