Instances locking and possible queuing

There is a need to lock different instances of nsfarm on same host to not influence them self. This is because they are for example exclusively using shared medium or loads non-exclusive shared medium.

The same code can also be used to wait for target to be released by some other instance instead of failing. That should be handy when we have multiple users on same server developing nsfarm as well as build system running tests on new builds.

• Implement general instance locking for resource
• Investigate non-blocking locking (like if you can't lock this return to this fixture later and try to lock it again instead of blocking) (probably is not possible)

With implementation done we should integrate it to

• Network performance tests (to have only one instance loading shared Ethernet connection)
• Access to Wi-Fi cards (no wifi yet)
• Test framework initialization with target blocked by some other instance.