Pick the random ports only once and try starting with them
a number of times so that the configuration can be re-used.
This is because the ports are written into the data files
and a subsequent agent reading the files needs to have the
same ports.
For the same reason we do not remove the data directory on
every attempt since this makes it impossible to re-read the
data files.
* don't use retry to try restarting the agent
this caused some issues when the startup would fail in
a separate go routine
* clear out the data directory on every retry since the ports
are stored in the raft data files
* set a unique id for every agent to allow for tracking of
concurrent output
This brings down the test run from 108 sec to 15 sec.
There is an occasional port conflict because of the nature
the next port is chosen. So far it seems rare enough to live
with it.
TestAgent will replace the following mechanisms to
start test agents in subsequent requests:
* makeAgentXXX
* makeDNSServerXXX
* makeHTTPServerXXX
* testServer
* httpTest
James Phillips