Summary:
If cmd.Env is passed, os.Environ() needs to be passed too. Otherwise, it does not read it.
Child process inherits the parent process env by default only if cmd.Env is passed. So, os.Environ() needs to be explicitly passed.

This was broken by https://phorge.dev.yugabyte.com/D53904 to remove the race in case of concurrent execution where the parent env can be overwritten by multiple calls (changed from the global parent os.Setenv to cmd.Env).

Test Plan:
itests must pass. (health-check failure).
UTs passed too.
Locally created a universe.

Reviewers: anijhawan, skhilar, spothuraju, dshubin

Reviewed By: dshubin

Subscribers: yugaware

Differential Revision: https://phorge.dev.yugabyte.com/D54468