sign_target_files_apks: Fix .prop string replacment

Value was being assigned unconditionally and causing a type mismatch (list and str)
Instead use a temporary value variable and only assign to value if the condition is
true.

Change-Id: I1b7d9dfd89321b23c51acf9fb19ceb37b530749e
Signed-off-by: Evan Anderson <evan1124@gmail.com>
Merge remote-tracking branch 'origin/kitkat' into kitkat
Full cache image generation

Port forward from here https://gerrit.paranoidandroid.co/#/c/99/ and here https://gerrit.paranoidandroid.co/#/c/103/

Checks goo for latest gapps package through its json api. If the api doesn't return anything, tries to get the link directly from the html. If it
fails too, it checks the /gapps folder to see if there's a package already downloaded.

Cache size can be changed in BoardConfig.mk with the var BOARD_CACHEIMAGE_SIZE (default is 500M).

Change-Id: Id6d125b5c5fd0d740eb4c3cf1cfd02ce19d9ea0a
Merge remote-tracking branch 'origin/kitkat' into kitkat
Merge remote-tracking branch 'upstream/kitkat' into kitkat