Add a flag to control deb-srcs and only add host bins to the chroot if the distro matches.
Add a flag to control deb-srcs and only add host bins to the chroot if the distro matches.

This fixes a problem on the Chrome buildbots where installing a hardy32 chroot
on a lucid64 machine results in 'ld' and other files in the chroot which do not
work because glibc is too old, and also prevents problems with apt-get fetching
from custom mirrors without source packages.

Review URL: http://codereview.chromium.org/3797014

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@63175 0039d316-1c4b-4281-b951-d872f2087c98

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