Ispn 3967/hotrod osgi feature

* created Karaf's features (in features.xml file) which allows for easy installation of the whole HotRod client 
package (including its dependencies) at once
* added tests for HotRod client running in Karaf
* several fixes for ISPN libraries in terms of exported/imported packages for OSGi

(if this PR is accepted, it might be good to add a chapter in ISPN docs, mentioning the Karaf's HotRod feature and the process of installation)