tests: option to override default migratable version

This patch gives user an option to override the
default migratable version to any later release.
This option makes MSHV specific tests suitable for
tests since MSHV is stable after some breaking changes.
This patch is also necessary for MSHV CI.

Signed-off-by: Muminul Islam <muislam@microsoft.com>

scripts/dev_cli.sh

@@ -538,6 +538,7 @@ cmd_tests() {
             --env TARGET_CC="$target_cc" \
             --env AUTH_DOWNLOAD_TOKEN="$AUTH_DOWNLOAD_TOKEN" \
             --env LLVM_PROFILE_FILE="$LLVM_PROFILE_FILE" \
+            --env MIGRATABLE_VERSION="$MIGRATABLE_VERSION" \
             "$CTR_IMAGE" \
             ./scripts/run_integration_tests_live_migration.sh "$@" || fix_dir_perms $? || exit $?
     fi