JMeter lib/ext directory configuration is ignored / not supported.

[Hugo Veillette]

Hi, following JMeter documentation  Apache JMeter - User's Manual: Getting Started , it is possible to use a directory other than the "JMETER_HOME/lib/ext" by providing "search_paths"  property.
This feature is quite handy when you want to ease JMeter upgrades, or have different users tapping in a single JMeter binary.

While the jmeter-plugin-manager will launch when placed in an user defined plugin directory, it will always try to download plugins in   "JMETER_HOME/lib/ext". 

Would it be possible to change the behavior here to allow for user defined directory?
A system property for instance would be acceptable.