Update myproxyclient Python package

[William-Hill]

According to @sashakames email, the myproxyclient Python package that is getting installed (version 2.0.1) is outdated and causing the publication test (and myproxy-logon) to fail. It should be upgraded to a newer version. Doing a pip install -U myproxyclient upgrades it to version 2.1.0.

Not sure what stage of the installation process the myproxyclient Python package gets installed so doing it during the bootstrap might cause the newer version to be overwritten. My have to do it downstream