Fix constraint violation exception when creating target with whitespaces (#363)

* Added a function to validate if controller id is empty

Signed-off-by: Jonathan Philip Knoblauch <JonathanPhilip.Knoblauch@bosch-si.com>

* Changed how the controller id gets past to other methods

Signed-off-by: Jonathan Philip Knoblauch <JonathanPhilip.Knoblauch@bosch-si.com>

* Changed the way controllderId gets validated in UI and repro

- added junit test

Signed-off-by: Jonathan Philip Knoblauch <JonathanPhilip.Knoblauch@bosch-si.com>

* Fixed sonar issue

Signed-off-by: Jonathan Philip Knoblauch <JonathanPhilip.Knoblauch@bosch-si.com>

* Switched to use the RegexpValidator 

Signed-off-by: Jonathan Philip Knoblauch <JonathanPhilip.Knoblauch@bosch-si.com>

hawkbit-repository/hawkbit-repository-jpa/src/main/java/org/eclipse/hawkbit/repository/jpa/model/JpaTarget.java

@@ -33,6 +33,7 @@ import javax.persistence.PrimaryKeyJoinColumn;
 import javax.persistence.Table;
 import javax.persistence.Transient;
 import javax.persistence.UniqueConstraint;
+import javax.validation.constraints.Pattern;
 import javax.validation.constraints.Size;
 
 import org.eclipse.hawkbit.im.authentication.SpPermission;
@@ -77,6 +78,7 @@ public class JpaTarget extends AbstractJpaNamedEntity implements Persistable<Lon
     @Column(name = "controller_id", length = 64)
     @Size(min = 1, max = 64)
     @NotEmpty
+    @Pattern(regexp = "[.\\S]*", message = "has whitespaces which are not allowed")
     private String controllerId;
 
     @Transient