Fix Benchpark use of current Ramble

[scheibelp]

Current Benchpark breaks w/ Ramble >= GoogleCloudPlatform/ramble@bab6ff3 (PR https://github.com/GoogleCloudPlatform/ramble/pull/428)

ramble -P -D <dir> workspace setup
==> Error: Command workspace does not exist.

(EDIT March 18: the second error described here has since been fixed in Ramble) installing Ramble's requirements.txt leads to another error:

ramble -P -D <dir> workspace setup
...
Environment saxpy references undefined package {modifier_package_name}

This is attempting to resolve these problems (but for now just addresses the first in CI).

[pearce8]

@scheibelp is this ready to be merged?

[scheibelp]

is this ready to be merged?

Not yet: Ramble has fixed the second problem. I wanted to consider whether we need to automatically install requirements.txt to handle the first

[scheibelp]

#196 does this more-robustly and has been merged.