for #23095 allow environment variables in core_{os}.cfg files
see https://github.com/shotgunsoftware/tk-core/pull/32
for #23095 expand env variables in the core_{os}.cfg files in tank shell script
address pull request comments
- add more descriptive comments with examples
- simplify env variable expansion by using os.path.expandvars() instead of using os.environ
- use double-quotes for consistency
- remove references to phantom logging objects
add comment to clarify this is Linux/OSX only functionality
Merge pull request #69 from shotgunsoftware/23095_env_var_expansion

for #23095 allow environment variables in core_{os}.cfg files
Merge branch 'master' into 25602_hook_by_name