[COMMON] Fix ${foo:3[:1]} bashisms

pointed out by checkbashisms

Issue-ID: OOM-264
Signed-off-by: Guillaume Lambert <guillaume.lambert@orange.com>
Change-Id: Ief3b2595a55f0e7a0a2e7ab05857848c99ce42f9
diff --git a/kubernetes/msb/components/msb-consul/resources/docker-entrypoint.sh b/kubernetes/msb/components/msb-consul/resources/docker-entrypoint.sh
index 0cd4616..cbcbf7a 100755
--- a/kubernetes/msb/components/msb-consul/resources/docker-entrypoint.sh
+++ b/kubernetes/msb/components/msb-consul/resources/docker-entrypoint.sh
@@ -53,7 +53,7 @@
 
 # If the user is trying to run Consul directly with some arguments, then
 # pass them to Consul.
-if [ "${1:0:1}" = '-' ]; then
+if echo "$1" | grep '^-' >/dev/null; then
     set -- consul "$@"
 fi