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

src/test/java/com/google/gwtorm/schema/sql/DialectMySQLTest.java

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 186134a..4f0b255 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");

src/test/java/com/google/gwtorm/schema/sql/DialectOracleSQLTest.java

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 8f75bb1..b7d501c 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");

src/test/java/com/google/gwtorm/schema/sql/DialectPostgreSQLTest.java

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 0330b18..6922aa5 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");