Skip invoking watch callback if the request is coming from the watch callback

Skip invoking watch callback if the request is coming from the watch callback

It is possible that request of acquiring/releasing focus can be executed within
focus watch callback. In this case, focus server can try to invoke the focus
watch callback of same node again based on conditions and then it gets blocked.
This patch avoids situation by skipping the callback again.

[Version] 0.11.2
[Issue Type] Enhancement

Change-Id: I2fc337227fa75dfb2d6f660fbc6c2fe4977b0548
Signed-off-by: Sangchul Lee <sc11.lee@samsung.com>