Run checkstyle plugin during package scope

1. Enable checkstyle verification during package phase. Currently it validates and writes result to console and target/checkstyle-result.xml files. 
2. Verification does not fail the build. Once all issues are fixed we can set `<failOnViolation>false</failOnViolation>` to true
3. Checkstyle rules are based on Falcon's rules, but with some modifications. Main modifications are - javadoc not required for package scope, allow package scope variables, local final not needed everywhere etc.
4. Some checks disabled for test code
It casues recursive project version definition
```
$ mvn clean package -DskipTests
[INFO] Scanning for projects...
[ERROR] The build could not read 1 project -> [Help 1]
[ERROR]
[ERROR]   The project org.apache.lens:checkstyle:${project.version} (/Users/jaideep.dhok/src/lens/checkstyle/pom.xml) has 4 errors
[ERROR]     Resolving expression: '${project.version}': Detected the following recursive expression cycle in 'project.version': [version] -> [Help 2]
[ERROR]     Resolving expression: '${project.version}': Detected the following recursive expression cycle in 'project.version': [version] -> [Help 2]
[ERROR]     Resolving expression: '${project.version}': Detected the following recursive expression cycle in 'project.version': [version] -> [Help 2]
[ERROR]     'build.plugins.plugin[org.apache.maven.plugins:maven-checkstyle-plugin].dependencies.dependency.version' for org.apache.lens:checkstyle:jar must be a valid version but is '${project.version}'. @ org.apache.lens:lens-parent:1.1.1-SNAPSHOT, src/lens/pom.xml, line 322, column 22
[ERROR]
[ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR]
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/ProjectBuildingException
[ERROR] [Help 2] http://cwiki.apache.org/confluence/display/MAVEN/InterpolationCycleException
```