Move to fixed nebula (#1550)

The repositories sometimes refer to snapshots and sometimes to the latest. To avoid nebula problems as we saw, I propose moving to a fixed nebula repository release 2.7.2.

I also resolved other potential problems in this area.

Author: wimjongman

io.sloeber.parent/pom.xml

@@ -351,7 +351,7 @@
 		<repository>
 			<id>nebula</id>
 			<layout>p2</layout>
-			<url>http://download.eclipse.org/nebula/releases/latest/</url>
+			<url>https://download.eclipse.org/nebula/releases/2.7.2/</url>
 		</repository>
 
 		<repository>

io.sloeber.product.sdk/arduino.product

@@ -280,13 +280,12 @@ United States, other countries, or both.
    </configurations>
 
    <repositories>
-      <repository location="http://download.eclipse.org/nebula/releases/latest/" enabled="true" />
-      <repository location="http://eclipse.baeyens.it/update/V4/nightly/" enabled="false" />
-      <repository location="http://eclipse.baeyens.it/update/V4/stable/" enabled="true" />
-      <repository location="http://gnu-mcu-eclipse.netlify.com/v4-neon-updates/" enabled="true" />
-      <repository location="http://download.eclipse.org/releases/latest/" enabled="true" />
-      <repository location="https://download.eclipse.org/technology/babel/update-site/latest/" enabled="true" />
-      <repository location="http://https://download.eclipse.org/justj/jres/15/updates/release/latest/" enabled="true" />
+      <repository location="https://eclipse.baeyens.it/update/V4/nightly/" enabled="false" />
+      <repository location="https://eclipse.baeyens.it/update/V4/stable/" enabled="true" />
+      <repository location="https://download.eclipse.org/technology/babel/update-site/latest/" enabled="false" />
+      <repository location="https://download.eclipse.org/nebula/releases/2.7.2/" enabled="true" />
+      <repository location="https://download.eclipse.org/justj/jres/17/updates/release/latest/" enabled="true" />
+      <repository location="https://download.eclipse.org/releases/latest/" enabled="true" />
       <repository location="https://download.eclipse.org/eclipse/updates/latest" enabled="true" />
    </repositories>