import pxssh from pexpect instead

[Zachary Ulissi]

pexpect can provide pxssh and is easy to find/install. pxssh is not available as a standalone package in pip/etc.

changing 'import pxssh' to 'from pexpect import pxssh' in utilities.py solves this problem and makes dependencies easier.

[andrew_peterson]

Depends on the version, I guess. On our cluster, it looks like pexpect is version 2.4 and it does not have this. On my ubuntu personal machine, pexpect is version 4.0.1 and does. So we would need some sort of version checking or try loop, as in

try:
    from pexpect import pxssh
except ImportError:
    import pxssh

which might be hard to remember to type as we import pxssh several places in the code (including within methods so that it isn't a requirement for serial processing). I wonder if there is a way to only have to implement the version checking once somewhere?

[andrew_peterson]

Allow pxssh to come from pexpect or pxssh package.

Addresses issue 61.

→ <<cset 27e7e3580193>>

[andrew_peterson]

I think I have allowed either import in commit 27e7e35.