docker: make sure debootstrap is at least 1.0.67

debootstrap prior to 1.0.67 generated an empty sources.list during
foreign bootstraps (Debian#732255 [1]). Fall back to the git checkout
if the installed debootstrap version is too old.

[1] https://bugs.debian.org/732255

Signed-off-by: Sascha Silbe <silbe@linux.vnet.ibm.com>
Message-Id: <1473192351-601-7-git-send-email-silbe@linux.vnet.ibm.com>
[Update 'sort -C' to 'sorc -c &>/dev/null' - Fam]
Signed-off-by: Fam Zheng <famz@redhat.com>
