Use the same variable for content addressing in functional tests

`CONTENT_ADDRESSED` -> `NIX_TESTS_CA_BY_DEFAULT`

tests/functional/build-remote-content-addressed-floating.sh

@@ -6,6 +6,6 @@ file=build-hook-ca-floating.nix
 
 enableFeatures "ca-derivations"
 
-CONTENT_ADDRESSED=true
+NIX_TESTS_CA_BY_DEFAULT=true
 
 source build-remote.sh

tests/functional/build-remote.sh

@@ -13,7 +13,7 @@ unset NIX_STATE_DIR
 function join_by { local d=$1; shift; echo -n "$1"; shift; printf "%s" "${@/#/$d}"; }
 
 EXTRA_SYSTEM_FEATURES=()
-if [[ -n "${CONTENT_ADDRESSED-}" ]]; then
+if [[ -n "${NIX_TESTS_CA_BY_DEFAULT-}" ]]; then
     EXTRA_SYSTEM_FEATURES=("ca-derivations")
 fi
 

tests/functional/ca/nix-shell.sh

@@ -2,6 +2,6 @@
 
 source common.sh
 
-CONTENT_ADDRESSED=true
+NIX_TESTS_CA_BY_DEFAULT=true
 cd ..
 source ./nix-shell.sh

tests/functional/nix-shell.sh

@@ -4,7 +4,7 @@ source common.sh
 
 clearStoreIfPossible
 
-if [[ -n ${CONTENT_ADDRESSED:-} ]]; then
+if [[ -n ${NIX_TESTS_CA_BY_DEFAULT:-} ]]; then
     shellDotNix="$PWD/ca-shell.nix"
 else
     shellDotNix="$PWD/shell.nix"