Enforce flush on CI test runs

Would be better handled by an explicity "clear manifest" task,
but that's the best we can do for now. Necessary because
of removed 'flush' setting from bootstrap.php, see
https://github.com/silverstripe/sapphire/pull/620

phpunit.teamcity.mssql.xml

@@ -18,14 +18,16 @@
 		</exclude>
 	</groups>
 
-	<!-- 
-		Set different database connection.
-		Relies on the presence of the 'zframeworktest_dbswitcher' module
-		(https://github.com/silverstripe-labs/zframeworktest_dbswitcher),
-		as well as on constants in _ss_environment.php (see module README).
-	-->
 	<php>
+		<!-- 
+			Set different database connection.
+			Relies on the presence of the 'zframeworktest_dbswitcher' module
+			(https://github.com/silverstripe-labs/zframeworktest_dbswitcher),
+			as well as on constants in _ss_environment.php (see module README).
+		-->
 	  <get name="db" value="mssql"/>
+	  <!-- Always flush the manifest -->
+	  <get name="flush" value="1"/>
 	</php>
 
 </phpunit>

phpunit.teamcity.postgresql.xml

@@ -18,14 +18,16 @@
 		</exclude>
 	</groups>
 
-	<!-- 
-		Set different database connection.
-		Relies on the presence of the 'zframeworktest_dbswitcher' module
-		(https://github.com/silverstripe-labs/zframeworktest_dbswitcher),
-		as well as on constants in _ss_environment.php (see module README).
-	-->
 	<php>
+		<!-- 
+			Set different database connection.
+			Relies on the presence of the 'zframeworktest_dbswitcher' module
+			(https://github.com/silverstripe-labs/zframeworktest_dbswitcher),
+			as well as on constants in _ss_environment.php (see module README).
+		-->
 	  <get name="db" value="postgresql"/>
+	  <!-- Always flush the manifest -->
+	  <get name="flush" value="1"/>
 	</php>
 
 </phpunit>

phpunit.teamcity.sqlite3.xml

@@ -18,14 +18,16 @@
 		</exclude>
 	</groups>
 
-	<!-- 
-		Set different database connection.
-		Relies on the presence of the 'zframeworktest_dbswitcher' module
-		(https://github.com/silverstripe-labs/zframeworktest_dbswitcher),
-		as well as on constants in _ss_environment.php (see module README).
-	-->
 	<php>
+		<!-- 
+			Set different database connection.
+			Relies on the presence of the 'zframeworktest_dbswitcher' module
+			(https://github.com/silverstripe-labs/zframeworktest_dbswitcher),
+			as well as on constants in _ss_environment.php (see module README).
+		-->
 	  <get name="db" value="sqlite3"/>
+	  <!-- Always flush the manifest -->
+	  <get name="flush" value="1"/>
 	</php>
 
 </phpunit>

phpunit.teamcity.xml

@@ -34,4 +34,5 @@
 			<group>sanitychecks</group>
 		</exclude>
 	</groups>
+	
 </phpunit>