Run update packages after fetching deb w/o source

- If we don't find a package's source, we fetch it from the last build's
package tarball. In the event that it was the last package fetched,
nothing would have updated the apt repo, so installing would fail at
rootfs time. Run after fetching from the prebuilt to
ensure that these packages are available.

Change-Id: I5e190bec70a100c2dc8b4a41afb429a3aa84f986
1 file changed