TST: run clipboard tests explicitly
closes #6317

@y-p u ok with this ... very simple
 Thanks. It's quieted down and it seems correlated with me logging in after all. 
Let's wait, it might have been me ruining things. disabling tests is a last resort.
 ok np
 Looks liks the errors were caused by logging in during building. closing for now.
The race window is real, but probably very small in practice.
 @jreback Here's the PR.
 righto thabks
 @cpcloud can you rebase this...these fail a lot on windows too....let's just disable
