Upgrade to bazel 0.7.0

0.7.0 came out.  This also contains patches to enable the network
namespace sandbox by default and require the sandbox.

Built from cb631f9bda3736c7818f593326209ed4327a27b4

Change-Id: I7e2899689ea3868f254ca60812fe35e0d7f6d218

tools/bazel

@@ -24,7 +24,7 @@ if [[ -n "${BAZEL_OVERRIDE+x}" ]]; then
   exec "${BAZEL_OVERRIDE}" "$@"
 fi
 
-readonly VERSION="0.6.1"
+readonly VERSION="0.7.0-971"
 
 readonly DOWNLOAD_DIR="$(dirname "${BASH_SOURCE[0]}")/../bazel-downloads"
 # Directory to unpack bazel into.  This must change whenever bazel changes.