Updated falcon-linux-install.sh

[David-M-Berry]

I have updated the falcon-linux-install.sh script with a "FALCON_DOWNLOAD_ONLY" option. Just like the other options, set it as an environment variable to 'true' and run the script. It will download the falcon sensor only, regardless of whether the sensor is already installed or not.

[carlosmmatos]

@David-M-Berry thanks for opening up this PR. I was literally going to create this same functionality today. If you don't mind, let's focus on the following:

• rebasing your changes on top of the latest updates
• only add the new functionality (ie, the stuff that makes the sensor download only work)
  • remove all other changes as those would be a different PR

I'd like to get this done by today if possible in order to drop a new release for recent updates. I'll go ahead and make the above changes and then we can start testing from there.

[David-M-Berry]

Sounds good @carlosmmatos. Let me know if you want any help in the testing (I've tested on Ubuntu and Redhat 9.3).