[COMMON] Fix ${!name} bashisms

pointed out by checkbashisms.

Note this kind of indirections can only be replaced directly in POSIX
by commands using eval.
Security risks must be evaluated for each context where eval is called.
For a safe use, the context must ensure that only a limited number of
possible constrainted values are passed to eval.

https://mywiki.wooledge.org/Bashism#Parameter_Expansions
https://mywiki.wooledge.org/BashFAQ/006#Indirection

Issue-ID: OOM-264
Signed-off-by: Guillaume Lambert <guillaume.lambert@orange.com>
Change-Id: Id27f3ffd1ddb092a9c038d3a45d9e3278720eb62
diff --git a/kubernetes/common/cassandra/resources/config/docker-entrypoint.sh b/kubernetes/common/cassandra/resources/config/docker-entrypoint.sh
index 5b65222..ff1908c 100644
--- a/kubernetes/common/cassandra/resources/config/docker-entrypoint.sh
+++ b/kubernetes/common/cassandra/resources/config/docker-entrypoint.sh
@@ -1,4 +1,5 @@
 #!/bin/bash
+
 set -e
 
 # first arg is `-f` or `--some-option`
@@ -71,7 +72,8 @@
                 authenticator \
         ; do
                 var="CASSANDRA_${yaml^^}"
-                val="${!var}"
+                # eval presents no security issue here because of limited possible values of var
+                eval val=\$$var
                 if [ "$val" ]; then
                         _sed-in-place "$CASSANDRA_CONFIG/cassandra.yaml" \
                                 -r 's/^(# )?('"$yaml"':).*/\2 '"$val"'/'
@@ -80,7 +82,8 @@
 
         for rackdc in dc rack; do
                 var="CASSANDRA_${rackdc^^}"
-                val="${!var}"
+                # eval presents no security issue here because of limited possible values of var
+                eval val=\$$var
                 if [ "$val" ]; then
                         _sed-in-place "$CASSANDRA_CONFIG/cassandra-rackdc.properties" \
                                 -r 's/^('"$rackdc"'=).*/\1 '"$val"'/'