Fix conditional unit test skipping

Change If4ae2aaec added assumeNoException calls in the test classes'
@Before annotated methods to skip testing for databases that are either
not installed or not properly configured on the system.

I29ab37e1c broke that, by moving database cleanup operation from setUp()
to tearDown(), but not taking into consideration, that when test was
skipped, executor wasn't properly instantiated and it come to NPE in
tearDown() method. Failures in tearDown() then caused test to be marked
as failed.

Change-Id: I6964feedbe44ad9849c4feaa2565d0089a84509a
diff --git a/src/test/java/com/google/gwtorm/schema/sql/DialectMaxDBTest.java b/src/test/java/com/google/gwtorm/schema/sql/DialectMaxDBTest.java
index 9bab614..2eb8cf4 100644
--- a/src/test/java/com/google/gwtorm/schema/sql/DialectMaxDBTest.java
+++ b/src/test/java/com/google/gwtorm/schema/sql/DialectMaxDBTest.java
@@ -92,6 +92,10 @@
 
   @After
   public void tearDown() {
+    if (executor == null) {
+      return;
+    }
+
     // Database content must be flushed because
     // tests assume that the database is empty
     drop("SEQUENCE address_id");
diff --git a/src/test/java/com/google/gwtorm/schema/sql/DialectMySQLTest.java b/src/test/java/com/google/gwtorm/schema/sql/DialectMySQLTest.java
index b0c8db5..7be69a4 100644
--- a/src/test/java/com/google/gwtorm/schema/sql/DialectMySQLTest.java
+++ b/src/test/java/com/google/gwtorm/schema/sql/DialectMySQLTest.java
@@ -81,6 +81,10 @@
 
   @After
   public void tearDown() {
+    if (executor == null) {
+      return;
+    }
+
     // Database content must be flushed because
     // tests assume that the database is empty
     drop("TABLE address_id");
diff --git a/src/test/java/com/google/gwtorm/schema/sql/DialectOracleSQLTest.java b/src/test/java/com/google/gwtorm/schema/sql/DialectOracleSQLTest.java
index bb4d7fb..16baae4 100644
--- a/src/test/java/com/google/gwtorm/schema/sql/DialectOracleSQLTest.java
+++ b/src/test/java/com/google/gwtorm/schema/sql/DialectOracleSQLTest.java
@@ -80,6 +80,10 @@
 
   @After
   public void tearDown() {
+    if (executor == null) {
+      return;
+    }
+
     // Database content must be flushed because
     // tests assume that the database is empty
     drop("SEQUENCE address_id");
diff --git a/src/test/java/com/google/gwtorm/schema/sql/DialectPostgreSQLTest.java b/src/test/java/com/google/gwtorm/schema/sql/DialectPostgreSQLTest.java
index aae302f..3b2ca6a 100644
--- a/src/test/java/com/google/gwtorm/schema/sql/DialectPostgreSQLTest.java
+++ b/src/test/java/com/google/gwtorm/schema/sql/DialectPostgreSQLTest.java
@@ -79,6 +79,10 @@
 
   @After
   public void tearDown() {
+    if (executor == null) {
+      return;
+    }
+
     // Database content must be flushed because
     // tests assume that the database is empty
     drop("SEQUENCE address_id");