USe `trueorfalse` for INSTALL_TESTONLY_PACKAGES

INSTALL_TESTONLY_PACKAGES is assumed to be set to `True` or `False`.
However, in devstack-gate this variable is set to 0 or 1. The patch uses
the already existing `trueorfalse` function to evaluate
INSTALL_TESTONLY_PACKAGES and normalize its value.

Change-Id: I0e4a31e422bad2a31d919d9f871e24833a0faa99
diff --git a/functions-common b/functions-common
index 48edba8..b9eaae5 100644
--- a/functions-common
+++ b/functions-common
@@ -993,6 +993,8 @@
     local file_to_parse
     local service
 
+    INSTALL_TESTONLY_PACKAGES=$(trueorfalse False $INSTALL_TESTONLY_PACKAGES)
+
     if [[ -z "$package_dir" ]]; then
         echo "No package directory supplied"
         return 1
@@ -1599,6 +1601,7 @@
         $cmd_pip install \
         $pip_mirror_opt $@
 
+    INSTALL_TESTONLY_PACKAGES=$(trueorfalse False $INSTALL_TESTONLY_PACKAGES)
     if [[ "$INSTALL_TESTONLY_PACKAGES" == "True" ]]; then
         local test_req="$@/test-requirements.txt"
         if [[ -e "$test_req" ]]; then