[Docker] Dgbuilder docker image does not build

Problem seems to be related to version of exec-maven-plugin - version 1.5.0 seems to work correctly

Change-Id: Iafde699687fb06ea1dfd9fa06b04668022007345
Signed-off-by: Timoney, Daniel (dt5972) <dtimoney@att.com>

Former-commit-id: 660e02d8d1fc4a06e756c068f36f9bf74aba3199
diff --git a/installation/admportal/pom.xml b/installation/admportal/pom.xml
index 5f5d221..7a45574 100644
--- a/installation/admportal/pom.xml
+++ b/installation/admportal/pom.xml
@@ -116,6 +116,7 @@
             <plugin>
                 <artifactId>exec-maven-plugin</artifactId>
                 <groupId>org.codehaus.mojo</groupId>
+		<version>1.5.0</version>
                 <executions>
                     <execution>
                         <id>Unzip admportal</id>