remotefilelog: avoid hard-coding pack names in tests
I'm about to alter the pack format, which alters the content-addressed
name of the pack file. In order to reduce my own confusion I found it
helpful to use an ls | head pipeline since we always want to inspect
the newest pack.
Differential Revision: https://phab.mercurial-scm.org/D4942
[workspace]
members = ["hgcli", "hg-core", "hg-direct-ffi"]
exclude = ["chg"]