ContactsCommon: fix import vcard memory leak

Spawining a bunch of imports at the same time will result in a SystemUI
crash due to hold on to Activity context beyond its lifecycle.

Change-Id: Id6e9a386bb19a1eb79377472b1bd1696c53d8bbf
Signed-off-by: Roman Birg <roman@cyngn.com>
Merge branch 'cm-11.0' of https://github.com/CyanogenMod/android_packages_apps_ContactsCommon into kitkat