containers/teuthology-dev/Dockerfile: fix running bootstrap

The `git config --unset` returns 5 if there is missing variable supposed
to be unset. Just always return true for this command so the bootstrap
can proceed.

Fixes: 7cc6ba4

Signed-off-by: Kyr Shatskyy <kyrylo.shatskyy@clyso.com>

Author: Kyr Shatskyy

containers/teuthology-dev/Dockerfile

@@ -31,7 +31,7 @@ RUN \
     PIP_INSTALL_FLAGS="-r requirements.txt" ./bootstrap
 COPY . /teuthology
 RUN \
-    git config -f ./.git/config --unset 'http.https://github.com/.extraheader' && \
+    (git config -f ./.git/config --unset 'http.https://github.com/.extraheader' || true ) && \
     ./bootstrap
 COPY containers/teuthology-dev/containerized_node.yaml /teuthology
 COPY containers/teuthology-dev/.teuthology.yaml /root