ARROW-2284: [Python] Fix error display on test_plasma error
ARROW-2284: [Python] Fix error display on test_plasma error

Just a trivial fix.  stderr is captured by py.test, not by the subprocess call.

Author: Antoine Pitrou <antoine@python.org>

Closes #1724 from pitrou/ARROW-2284 and squashes the following commits:

46a692c9 <Antoine Pitrou> ARROW-2284:  Fix error display on test_plasma error

cpcloud/arrow,wagavulin/arrow,xhochy/arrow,itaiin/arrow,wesm/arrow,renesugar/arrow,dremio/arrow,cpcloud/arrow,pcmoritz/arrow,wesm/arrow,dremio/arrow,icexelloss/arrow,wesm/arrow,wagavulin/arrow,kou/arrow,dremio/arrow,majetideepak/arrow,tebeka/arrow,renesugar/arrow,yufeldman/arrow,itaiin/arrow,renesugar/arrow,wesm/arrow,apache/arrow,majetideepak/arrow,laurentgo/arrow,laurentgo/arrow,kou/arrow,cpcloud/arrow,yufeldman/arrow,cpcloud/arrow,renesugar/arrow,kou/arrow,pcmoritz/arrow,cpcloud/arrow,itaiin/arrow,wagavulin/arrow,tebeka/arrow,apache/arrow,majetideepak/arrow,wagavulin/arrow,majetideepak/arrow,apache/arrow,xhochy/arrow,laurentgo/arrow,kou/arrow,wagavulin/arrow,icexelloss/arrow,majetideepak/arrow,renesugar/arrow,apache/arrow,xhochy/arrow,icexelloss/arrow,icexelloss/arrow,itaiin/arrow,cpcloud/arrow,xhochy/arrow,icexelloss/arrow,pcmoritz/arrow,majetideepak/arrow,itaiin/arrow,apache/arrow,tebeka/arrow,renesugar/arrow,tebeka/arrow,itaiin/arrow,dremio/arrow,pcmoritz/arrow,kou/arrow,icexelloss/arrow,cpcloud/arrow,majetideepak/arrow,wesm/arrow,xhochy/arrow,tebeka/arrow,dremio/arrow,pcmoritz/arrow,majetideepak/arrow,laurentgo/arrow,tebeka/arrow,xhochy/arrow,itaiin/arrow,wesm/arrow,icexelloss/arrow,laurentgo/arrow,laurentgo/arrow,wagavulin/arrow,renesugar/arrow,wagavulin/arrow,renesugar/arrow,icexelloss/arrow,renesugar/arrow,apache/arrow,wesm/arrow,kou/arrow,dremio/arrow,itaiin/arrow,dremio/arrow,xhochy/arrow,tebeka/arrow,icexelloss/arrow,renesugar/arrow,icexelloss/arrow,kou/arrow,cpcloud/arrow,itaiin/arrow,yufeldman/arrow,wagavulin/arrow,majetideepak/arrow,pcmoritz/arrow,itaiin/arrow,yufeldman/arrow,renesugar/arrow,yufeldman/arrow,majetideepak/arrow,cpcloud/arrow,tebeka/arrow,renesugar/arrow,majetideepak/arrow,yufeldman/arrow,cpcloud/arrow,apache/arrow,kou/arrow,dremio/arrow,xhochy/arrow,majetideepak/arrow,itaiin/arrow,dremio/arrow,renesugar/arrow,xhochy/arrow,wesm/arrow,yufeldman/arrow,apache/arrow,apache/arrow,majetideepak/arrow,itaiin/arrow,pcmoritz/arrow,kou/arrow,laurentgo/arrow,icexelloss/arrow,pcmoritz/arrow,wagavulin/arrow,itaiin/arrow,apache/arrow,yufeldman/arrow,apache/arrow,xhochy/arrow,pcmoritz/arrow,dremio/arrow,apache/arrow,apache/arrow,majetideepak/arrow,xhochy/arrow,laurentgo/arrow,xhochy/arrow,wesm/arrow,majetideepak/arrow,renesugar/arrow,renesugar/arrow,xhochy/arrow,itaiin/arrow,kou/arrow,yufeldman/arrow,pcmoritz/arrow,icexelloss/arrow,laurentgo/arrow,kou/arrow,cpcloud/arrow,laurentgo/arrow,tebeka/arrow,tebeka/arrow,cpcloud/arrow,cpcloud/arrow,wagavulin/arrow,wagavulin/arrow,icexelloss/arrow,kou/arrow,pcmoritz/arrow,laurentgo/arrow,wesm/arrow,yufeldman/arrow,wesm/arrow,xhochy/arrow,cpcloud/arrow,wesm/arrow,yufeldman/arrow,icexelloss/arrow,laurentgo/arrow,laurentgo/arrow,kou/arrow,pcmoritz/arrow,pcmoritz/arrow,dremio/arrow,laurentgo/arrow,xhochy/arrow,kou/arrow,pcmoritz/arrow,wesm/arrow,wesm/arrow,laurentgo/arrow,pcmoritz/arrow,apache/arrow,itaiin/arrow,wagavulin/arrow