Store the value from TARGET_OTA_ASSERT_DEVICE to a file

This is needed so it can be read in when re-signing a package to
allow for the proper device asserts.

Change-Id: I8f3bb491bbbaa4d2b827a45ef83f12c6c83e6712
Merge "Store the value from TARGET_OTA_ASSERT_DEVICE to a file" into cm-11.0
Merge branch 'cm-11.0' of https://github.com/CyanogenMod/android_build into kk44