Fix the VpnDialog for device orientation

STEPS TO REPRODUCE:
1) Connect the VPN
2) Show the connected VPN information through tha VpnDialog App.
3) Orientation Change
4) Dismiss the connected VPN information(ManageDialog)

root cause :
If orientation is changed, always excute finish() method in onPause()

solution :
In ManageDialog, if the user change the device's orientation,
check the configuration change and avoid the finish() in onPause().
And add the mIsShown variable which check the exist dialog.

Change-Id: I93dccc0b10b2e81ca14f1230651f1211282914bf
Signed-off-by: SangJin Cha <sj.cha@lge.com>