Gateway should be singleton, not a prototype
NEXUS-7515: ITs static port use removed

Now the port is dynamic as for any other ITs,
lessening the failure probability on CI and other
cases.

Also, the ITs were writing to src/test/it-resources
(the reason why .gitignore was there), that is
not the case anymore
Revert "Gateway should be singleton, not a prototype"

This reverts commit e4a6ae325041b82711f13d9fcb31250e54f647e1.
Merge pull request #767 from sonatype/NEXUS-7515-ruby-nx-port

NEXUS-7515: ITs static port use