Improve the handling of the TLS certifiactes

[mbwhite]

For reasons lost in history, Fabric hasn't standised on whether to load certs in base64 or PEM format. What does seem to be standard is if the environment variable ends in FILE then it's a PEM format, but if it's PATH then it's base64.

This change will allow either FILE or PATH environment variables to be used in all cases.

Signed-off-by: Matthew B White [email protected]