LPS-48916 Liferay 6.2 Solr plugin only allows 2 threads, and configuring it to a higher value with throw an NPE

Hello @hhuijser,

I'm reopening the same pull request for LPS-48916.

@mhan810

There's a bug in our build process that I will look into, but here's a recap:
We're compiling solr4-web with liferay's 4.3.3 httpclient.jar, but during deployment, solr4web is using its 4.2.3 httpclient.jar. Until we update the jars in solr to 4.3+, the code that we're using in this pull request is actually not deprecated (Liferay only thinks that it is). I am working with @holatuwol to fix this issue with our build process, but until we do, this commit should work.