Update checkstyle plugin dependency config

The problem is that, even though the Checkstyle plugin config in the jclouds-project profile is correctly applied, the effective POM in jclouds-project _still_ contains the dependency, even though it doesn't need it:

      <plugin>
        <artifactId>maven-checkstyle-plugin</artifactId>
        <version>2.11</version>
        <dependencies>
          <dependency>
            <groupId>org.apache.jclouds</groupId>
            <artifactId>jclouds-resources</artifactId>
            <version>1.7.2-SNAPSHOT</version>
            <scope>compile</scope>
          </dependency>
        </dependencies>
        <configuration>
          <configLocation>../resources/checkstyle.xml</configLocation>
          <violationSeverity>warning</violationSeverity>
          <includeTestSourceDirectory>true</includeTestSourceDirectory>
        </configuration>
      </plugin>

(from `mvn help:effective-pom` in jclouds/project). This has been causing the CI builds to fail after a release because jclouds-project, which is the _first_ project to be built, needs this dep and can't find it (it's also looking in the wrong repo - hence the second commit).

After the change, things look better. In jclouds/project:

      <plugin>
        <artifactId>maven-checkstyle-plugin</artifactId>
        <version>2.11</version>
        <configuration>
          <configLocation>../resources/checkstyle.xml</configLocation>
          <violationSeverity>warning</violationSeverity>
          <includeTestSourceDirectory>true</includeTestSourceDirectory>
        </configuration>
      </plugin>

In jclouds/core:

      <plugin>
        <artifactId>maven-checkstyle-plugin</artifactId>
        <version>2.11</version>
        <dependencies>
          <dependency>
            <groupId>org.apache.jclouds</groupId>
            <artifactId>jclouds-resources</artifactId>
            <version>1.8.0-SNAPSHOT</version>
            <scope>compile</scope>
          </dependency>
        </dependencies>
        <configuration>
          <configLocation>resources/checkstyle.xml</configLocation>
          <violationSeverity>warning</violationSeverity>
          <includeTestSourceDirectory>true</includeTestSourceDirectory>
        </configuration>
      </plugin>