This change now allows the user to specify the ostree repository he
wishes to use as base for the pre-patched ISO.
Test plan:
PASS: Build pre-patched ISO with default ostree repository
PASS: Build pre-patched ISO with specific ostree repository
Partial-Bug: 2090871
Change-Id: I52845b2a633b30f3407a3e2a65edd2ba088b63c7
Signed-off-by: Dostoievski Batista <dostoievski.albinobatista@windriver.com>