SPARK-2879 [BUILD] Use HTTPS to access Maven Central and other repos

Maven Central has just now enabled HTTPS access for everyone to Maven Central (http://central.sonatype.org/articles/2014/Aug/03/https-support-launching-now/) This is timely, as a reminder of how easily an attacker can slip malicious code into a build that's downloading artifacts over HTTP (http://blog.ontoillogical.com/blog/2014/07/28/how-to-take-over-any-java-developer/).

In the meantime, it looks like the Spring repo also now supports HTTPS, so can be used this way too.

I propose to use HTTPS to access these repos.

Author: Sean Owen <srowen@gmail.com>

Closes #1805 from srowen/SPARK-2879 and squashes the following commits:

7043a8e [Sean Owen] Use HTTPS for Maven Central libs and plugins; use id 'central' to override parent properly; use HTTPS for Spring repo

pom.xml

@@ -143,11 +143,11 @@
 
   <repositories>
     <repository>
-      <id>maven-repo</id>
+      <id>central</id>
       <!-- This should be at top, it makes maven try the central repo first and then others and hence faster dep resolution -->
       <name>Maven Repository</name>
       <!-- HTTPS is unavailable for Maven Central -->
-      <url>http://repo.maven.apache.org/maven2</url>
+      <url>https://repo.maven.apache.org/maven2</url>
       <releases>
         <enabled>true</enabled>
       </releases>
@@ -213,7 +213,7 @@
     <repository>
       <id>spring-releases</id>
       <name>Spring Release Repository</name>
-      <url>http://repo.spring.io/libs-release</url>
+      <url>https://repo.spring.io/libs-release</url>
       <releases>
         <enabled>true</enabled>
       </releases>
@@ -222,6 +222,15 @@
       </snapshots>
     </repository>
   </repositories>
+  <pluginRepositories>
+    <pluginRepository>
+      <id>central</id>
+      <url>https://repo1.maven.org/maven2</url>
+      <releases>
+        <enabled>true</enabled>
+      </releases>
+    </pluginRepository>
+  </pluginRepositories>
 
   <dependencyManagement>
     <dependencies>