nmAPI to except RepyArgumentError's on calling emulfile.check_repy_filename

(Note: This is a re-commit of aaaaalbert@312af3fdb40f4e0fc22b9442059dcbd7acb9fc64,
made to use the correct parent commit for easier merging with
SeattleTestbed/nodemanager's master branch).

nmAPI `except`ed TypeError's before, and thus never caught anything,
resulting in the RepyArgumentError reaching callers like the
`nmrequesthandler` (line 111) and missing clauses for the appropriate e
errors. This would cause a nodemanager to report an "Internal Error"
with no further details, as could be observed by uploading through
`seash` a file conflicting with `emulfile`'s filename checks (disallowed
characters, name starting with "." or "private_", name too long).

Thanks go to Rohan Dalvi for reporting the issue!