Allow a configurable credentials directory

[devaidendale]

This adds an IHUB_CREDS_DIR environment variable for choosing where the developer scripts load Flow credentials. Existing installations continue to use ~/creds by default.

It also makes uploadRecipe.sh use its Bash execution contract and resolve setEnvForUpload.sh from the script directory, so loading its sibling helper does not depend on the caller's working directory.

• Apply the configured directory to upload and token-management scripts.
• Quote credential paths when loading environment-specific files.
• Run uploadRecipe.sh under Bash and exit cleanly on invalid invocations.
• Resolve shared upload environment setup relative to uploadRecipe.sh.

[devaidendale]

(This is partially related to Sous/PIA work -- but seemed like a good idea to fold in regardless.)