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>
ccache: Use system version over prebuilt

If there is a ccache binary on the
host system use it instead of the
AOSP prebuilt.

Change-Id: I4b1e030713be22167a12bd229a4e35eda7736cd2
Signed-off-by: Evan Anderson <evan1124@gmail.com>