Use 'tempest run --slowest' in integrated-compute

This adds the '--slowest' option to the 'tempest run' command line for
the [testenv:integrated-compute] to show the slowest tests after the
tests finish running.

Change-Id: I53b0fa6dcf077191565e2aaf3f08a24b3238a34b
diff --git a/tox.ini b/tox.ini
index de81707..c90201e 100644
--- a/tox.ini
+++ b/tox.ini
@@ -198,7 +198,7 @@
 commands =
     find . -type f -name "*.pyc" -delete
     tempest run --regex {[testenv:integrated-compute]regex1} --exclude-list ./tools/tempest-integrated-gate-compute-exclude-list.txt {posargs}
-    tempest run --combine --serial --regex {[testenv:integrated-compute]regex2} --exclude-list ./tools/tempest-integrated-gate-compute-exclude-list.txt {posargs}
+    tempest run --combine --serial --slowest --regex {[testenv:integrated-compute]regex2} --exclude-list ./tools/tempest-integrated-gate-compute-exclude-list.txt {posargs}
 
 [testenv:integrated-placement]
 envdir = .tox/tempest