Add explanatory prefix to post_test_perf output

The pirate on crack output of placeload can be confusing
so this change adds a prefix to the placement-perf.txt log
file so that it is somewhat more self-explanatory.

This change also pins the version of placeload because the
explanation is version dependent.

Change-Id: I055adb5f6004c93109b17db8313a7fef85538217

gate/post_test_perf_check.sh

@@ -1,6 +1,31 @@
 #!/bin/bash -x
 
 # Do some performance related information gathering for placement.
+EXPLANATION="
+This output combines output from placeload with timing information
+gathered via curl. The placeload output is the current maximum
+microversion of placement followed by an encoded representation of
+what it has done. Lowercase 'r', 'i', and 'a' indicate successful
+creation of a resource provider, inventory and aggregate. If
+there are upper case versions of any of those letters, a failure
+happened for a single request. The letter will be followed by the
+HTTP status code and the resource provider uuid. These can be used
+to find the relevant entry in logs/screen-placement-api.txt.gz.
+
+Note that placeload does not exit with an error code when this
+happens. It merely reports and moves on. Under correct circumstances
+the right output is a long string of 3000 characters containing
+'r', 'i', 'a' in random order (because async).
+
+After that are three aggregate uuids, and then the output
+of two timed curl requests.
+
+If no timed requests are present it means that the expected number
+of resource providers was not created. At this time, only resource
+providers are counted, not whether they have inventory or aggregates.
+
+"
+
 
 # This aggregate uuid is a static value in placeload.
 AGGREGATE="14a5c8a3-5a99-4e8f-88be-00d85fcb1c17"
@@ -22,7 +47,7 @@ function check_placement {
     . .placeload/bin/activate
 
     # install placeload
-    pip install placeload
+    pip install 'placeload==0.2.2'
 
     # Turn off keystone auth
     iniset -sudo $NOVA_CONF DEFAULT auth_strategy noauth2
@@ -32,7 +57,10 @@ function check_placement {
     placement_url=$(get_endpoint_url placement public)
 
     # load with placeload
-    placeload $placement_url $COUNT | tee -a $LOG
+    (
+        echo "$EXPLANATION"
+        placeload $placement_url $COUNT
+    ) | tee -a $LOG
     rp_count=$(curl -H 'x-auth-token: admin' $placement_url/resource_providers |json_pp|grep -c '"name"')
     # Skip curl and note if we failed to create the required number of rps
     if [[ $rp_count -ge $COUNT ]]; then