Upgrade findbugs maven plugin to 3.0.4

Depending on Maven version the Findbugs plugin version 3.0.0 can produce this:

[ERROR] Failed to execute goal org.codehaus.mojo:findbugs-maven-plugin:3.0.0:findbugs (default) on project hbase: Unable to parse configuration of mojo org.codehaus.mojo:findbugs-maven-plugin:3.0.0:findbugs for parameter pluginArtifacts: Cannot assign configuration entry 'pluginArtifacts' with value '${plugin.artifacts}' of type java.util.Collections.UnmodifiableRandomAccessList to property of type java.util.ArrayList -> [Help 1]

Fix is to upgrade the plugin from 3.0.0 to 3.0.4.

This looks like an issue only with the branch-1s.