Merge #18798: ci: Fix default retry script usage

45615de26c ci: Fix default retry script usage (Hennadii Stepanov)

Pull request description:

  On master (5352d14b37) `CI_RETRY_EXE=${CI_RETRY_EXE:retry}` works as a [Substring Expansion](https://www.gnu.org/software/bash/manual/html_node/Shell-Parameter-Expansion.html), and that is wrong.
  If `CI_RETRY_EXE` variable was unset initially, its new value becomes an empty string, but not "retry" as one could expect. Consequently, the `${CI_RETRY_EXE} ...` command does _not_ use `ci/retry/retry` script.

  This PR makes for `CI_RETRY_EXE` variable a usual parameter expansion, i.e., `${parameter:-word}`.

  Reference: https://github.com/bitcoin/bitcoin/pull/18735#issuecomment-620095489

Top commit has no ACKs.

Tree-SHA512: 108173f6b2677979b9ddf2f9b9df4a6c56f5efa81c36543a1816bb3b984e42984bf3c83fe413ea3a5ca1e2317c4efb02fea7180a6b44863af7cfe6202e9cf94d

ci/test/00_setup_env.sh

@@ -59,4 +59,4 @@ export DOCKER_PACKAGES=${DOCKER_PACKAGES:-build-essential libtool autotools-dev
 export GOAL=${GOAL:-install}
 export DIR_QA_ASSETS=${DIR_QA_ASSETS:-${BASE_SCRATCH_DIR}/qa-assets}
 export PATH=${BASE_ROOT_DIR}/ci/retry:$PATH
-export CI_RETRY_EXE=${CI_RETRY_EXE:retry}
+export CI_RETRY_EXE=${CI_RETRY_EXE:-"retry --"}

ci/test/04_install.sh

@@ -58,6 +58,7 @@ else
     bash -c "export PATH=$BASE_SCRATCH_DIR/bins/:\$PATH && cd $P_CI_DIR && $*"
   }
 fi
+export -f DOCKER_EXEC
 
 if [ -n "$DPKG_ADD_ARCH" ]; then
   DOCKER_EXEC dpkg --add-architecture "$DPKG_ADD_ARCH"