Don't write files to local ~/.ssh/

We should avoid writing temporary files to the local user's ~/.ssh/
directory. Store private key for test environment in envs/test and
safely create a controlmasters directory for ssh mux sockets.
Create /envs/test/ if not present
Use umask to write key with correct permissions

Alter umask before writing key, then write key and restore umask rather
than writing key with incorrect permissions then go back and fix
permissions.
Fix storing private key in envs/test/
Merge pull request #134 from blueboxgroup/avoid-using-users-ssh-dir

Avoid using user's ssh dir for temporary test files