ClassLoader issue in embedded Arquillian

[jbescos]

Fixes Issue
helidon-io/helidon#6884

Related Issue(s)
helidon-io/helidon#6884

Describe the change
Using embedded Arquillian, there is only one JVM, so next line will not get the resource from the web application, it will get the test execution classpath (the file will not be found):
getClass().getResourceAsStream("/key.pub")
This suggested fix is more flexible, because the web container is able to set its own class loader.

Additional context
I faced this issue integrating this in Helidon.

CC @alwin-joseph @anajosep @arjantijms @cesarhernandezgt @dblevins @m0mus @edbratt @gurunrao @jansupol @jgallimore @kazumura @kwsutter @LanceAndersen @bhatpmk @RohitKumarJain @shighbar @gthoman @brideck @OndroMih @dmatej
@starksm64 @scottmarlow

[arjantijms]

p.s. for Piranha Cloud and Arquillian I worked on an isolated class loader so tests won't pick up thing from the environment. Might be worthwhile to see if that can be applied to this situation as well at some point.