Don't remove yugabyte-bash-common when performing a clean build

Summary:
Don't remove yugabyte-bash-common when performing a clean build.
We were removing the entire build directory when doing a clean-all build, which also
removed yugabyte-bash-common which is already been sourced into the current bash context.
It isn't possible to modify yugabyte-bash-common during a build, it can only be sourced once.
So don't delete it when cleaning the build env.

Test Plan:
jenkins
Ran `yb_build.sh --clean-all` multiple times to ensure everything except yugabyte-bash-common is
deleted.

Reviewers: devops, steve.varnau

Reviewed By: steve.varnau

Subscribers: devops

Differential Revision: https://phorge.dev.yugabyte.com/D40151

yb_build.sh

@@ -925,7 +925,8 @@ fi
 
 if [[ ${remove_entire_build_dir_before_build} == "true" ]]; then
   log "Removing the entire ${YB_SRC_ROOT}/build directory (--clean-all specified)"
-  ( set -x; rm -rf "${YB_SRC_ROOT}/build" )
+  ( set -x; find "${YB_SRC_ROOT}/build" -maxdepth 1 -mindepth 1 \
+      ! -name "yugabyte-bash-common" -exec rm -rf {} \; )
   save_paths_and_archive_urls_to_build_dir
 elif [[ ${remove_build_root_before_build} == "true" ]]; then
   log "Removing '$BUILD_ROOT' (--clean specified)"