Install Tempest's dependencies along with it.

* lib/tempest(install_tempest): Directly install Tempest's
tools/pip-requires list after cloning the repo.

Change-Id: I5c508faab8756d5cdfec53193e08e3440fda1b2c
diff --git a/lib/tempest b/lib/tempest
index 115c911..871e9e7 100644
--- a/lib/tempest
+++ b/lib/tempest
@@ -49,6 +49,10 @@
 # install_tempest() - Collect source and prepare
 function install_tempest() {
     git_clone $TEMPEST_REPO $TEMPEST_DIR $TEMPEST_BRANCH
+
+    # Tempest doesn't satisfy its dependencies on its own, so
+    # install them here instead.
+    sudo pip install -r $TEMPEST_DIR/tools/pip-requires
 }