Fix some warnings with plugin maven-failsafe-plugin

[baudoliver7]

When we run integration tests, we see these warnings :

[WARNING] useSystemClassLoader setting has no effect when not forking
[WARNING] The parameter forkCount should likely not be 0, not forking a JVM for tests reduce test accuracy, ensure to have a <forkCount> >= 1.

See : artipie/asto#380 (comment)