e_client: Unset current focus when the new focusable ec found

e_client: Unset current focus when the new focusable ec found

There was a bug that couldn't receive focus changed event when client unobscured by activate using topmost focus policy.

For more detail, in topmost focus policy, issues following below sequence.
1. Focused window(winA) requests Activate below to fully obscured window(winB).
2. winA requests Activate before winB showing.

The Activate below request didn't doing uniconify render, so stack was changed immediately.
and it cause visiblity changes immediately and visibility changed event send to each client.

The winB didn't focused because of the winB is not shown till the uniconify rendering by visibility.
in this case, winA still focused but winA is not focusable window before winB shown or winA Activated.

It can cause the client didn't receive focus changed event after the client unobscured.
(client regards the fully-obscured means loose focus)

for fix this problem, always focus unset before focused window when there're new focusable window.

Change-Id: Iaccfa5ed77bd46f58a4f82acd9109e534da54606