prefixArgs uses os.Setenv in e2e tests instead envMap.
This creates overwrites in some test cases and have an impact
on test quality and isolation between tests.
This PR uses ctlcontext envMap in each tests with high priority
and merges os environment variables with low priority.
This change makes the etcd package compatible with the existing Go
ecosystem for module versioning.
Used this tool to update package imports:
https://github.com/KSubedi/gomove
