Update: I compiled the libssh2 simple example programs ssh2_exec and ssh2 and ran them against both the system libssh2 and the puppet enterprise libssh2 libraries. Both programs work with the system libssh2 library. While ssh2_exec works with the puppet libssh2 library, the ssh2 program fails with the puppet libssh2 library. So, at least I have some way to reproduce/test/debug outside of puppet enterprise now. Oddly, while I thought it would fail with the public key auth, it also fails with password auth... The mystery continues.