Fix misleading STATUS_CLIENT warning message

After Tor 0.4.3.0-alpha-dev successfully established a TCP connection with a bridge but failed to finish its handshake, it sends the following STATUS_CLIENT message to the controller:

650 STATUS_CLIENT WARN BOOTSTRAP PROGRESS=10 TAG=handshake_dir SUMMARY="Finishing handshake with directory server" WARNING="DONE" REASON=DONE COUNT=1 RECOMMENDATION=warn HOSTID="0000000000000000000000000000000000000000" HOSTADDR="[scrubbed]"

One can reproduce this by using torproject.org's web server as a bridge: 95.216.163.36:80. The substring WARNING="DONE" is misleading and should – if I'm interpreting control-spec.txt correctly – contain a human-readable description of what went wrong. Other STATUS_CLIENT messages do a better job; for example:

650 STATUS_CLIENT WARN BOOTSTRAP PROGRESS=5 TAG=conn_dir SUMMARY="Connecting to directory server" WARNING="Connection refused" REASON=CONNECTREFUSED COUNT=1 RECOMMENDATION=warn HOSTID="0000000000000000000000000000000000000000" HOSTADDR="[scrubbed]"

Here, the substring WARNING="Connection refused" gives me a good idea of what's going on.

I suggest to fix the warning in this particular error case.