Added missing quote marks to TEST_PREFIX (GoogleCloudPlatform#10035)

Without this, | gets interpreted as a pipe and the test count always becomes 0 if there are multiple prefixes supplied

mmv1/third_party/terraform/.teamcity/components/builds/build_steps.kt

@@ -118,7 +118,7 @@ fun BuildSteps.runAcceptanceTests() {
                   exit 0
                 fi
                 
-                export TEST_COUNT=${'$'}(./test-binary -test.list=%TEST_PREFIX% | wc -l)
+                export TEST_COUNT=${'$'}(./test-binary -test.list="%TEST_PREFIX%" | wc -l)
                 echo "Found ${'$'}{TEST_COUNT} tests that match the given test prefix %TEST_PREFIX%"
                 if test ${'$'}TEST_COUNT -le "0"; then
                   echo "Skipping test execution; no tests to run"