BUG-529: Remove Reactor getter contention

Performance testing has identified contention on getInstance() methods.
It turns out that we can pre-create the instance and then get it in a
lock-free manner.

(cherry picked from commit 9fe23c3d6e9db28fa7ad14a1949b3add13b9015d)
Signed-off-by: Robert Varga <robert.varga@pantheon.sk>
Signed-off-by: Michal Rehak <mirehak@cisco.com>
Change-Id: Iba47dc979efd0b80ea213b8410ce51218aed8beb